diff --git a/src/ast.ts b/src/ast.ts
index 0158656..da6cd8c 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -101,7 +101,7 @@ export class Node {
             case "IndexExpr":
                 return visit(k.value, k.arg);
             case "CallExpr":
-                return visit(k.value, ...k.args);
+                return visit(k.value, ...k.generics ?? [], ...k.args);
             case "UnaryExpr":
                 return visit(k.expr);
             case "BinaryExpr":
@@ -117,6 +117,8 @@ export class Node {
                 return visit(k.ty, k.length);
             case "SliceTy":
                 return visit(k.ty);
+            case "Generic":
+                return visit();
         }
         k satisfies never;
     }
@@ -131,6 +133,7 @@ export type NodeKind =
     | {
         tag: "FnStmt";
         ident: string;
+        genericParams: Node[] | null;
         params: Node[];
         retTy: Node | null;
         body: Node;
@@ -146,7 +149,7 @@ export type NodeKind =
     | { tag: "StrExpr"; value: string }
     | { tag: "ArrayExpr"; values: Node[] }
     | { tag: "IndexExpr"; value: Node; arg: Node }
-    | { tag: "CallExpr"; value: Node; args: Node[] }
+    | { tag: "CallExpr"; value: Node; generics: Node[] | null; args: Node[] }
     | { tag: "UnaryExpr"; op: UnaryOp; expr: Node; tok: string }
     | { tag: "BinaryExpr"; op: BinaryOp; left: Node; right: Node; tok: string }
     | {
@@ -158,7 +161,8 @@ export type NodeKind =
     | { tag: "IdentTy"; ident: string }
     | { tag: "PtrTy" | "PtrMutTy"; ty: Node }
     | { tag: "ArrayTy"; ty: Node; length: Node }
-    | { tag: "SliceTy"; ty: Node };
+    | { tag: "SliceTy"; ty: Node }
+    | { tag: "Generic"; ident: string };
 
 export type IntTy =
     | "i8"
diff --git a/src/front/check.ts b/src/front/check.ts
index 45f5d92..0831f2b 100644
--- a/src/front/check.ts
+++ b/src/front/check.ts
@@ -61,6 +61,7 @@ export class CheckedFn {
 
 class TypeChecker {
     private nodeTys = new Map<ast.Node, Ty>();
+    private generics?: Ty[];
     private params!: Ty[];
 
     constructor(
@@ -71,6 +72,12 @@ class TypeChecker {
     ) {}
 
     check(): CheckedFn {
+        const generics = this.fn.kind.genericParams
+            ?.map((_node, idx) => {
+                return Ty.Generic(idx);
+            });
+        this.generics = generics;
+
         const params = this.fn.kind.params
             .map((node) => {
                 const param = node.as("Param");
@@ -194,6 +201,7 @@ class TypeChecker {
                     case "PtrMutTy":
                     case "ArrayTy":
                     case "SliceTy":
+                    case "Generic":
                         break;
                     default:
                         k satisfies never;
@@ -205,7 +213,7 @@ class TypeChecker {
 
         const ty = Ty.create("FnStmt", {
             stmt: this.fn,
-            ty: Ty.create("Fn", { params, retTy }),
+            ty: Ty.Fn(params, retTy, generics ?? null),
         });
 
         return new CheckedFn(ty, this.nodeTys);
@@ -250,24 +258,6 @@ class TypeChecker {
     private checkExpr(expr: ast.Node, expected: Ty): Ty {
         const k = expr.kind;
         switch (k.tag) {
-            case "Error":
-            case "File":
-            case "Block":
-            case "ExprStmt":
-            case "AssignStmt":
-            case "FnStmt":
-            case "ReturnStmt":
-            case "LetStmt":
-            case "IfStmt":
-            case "WhileStmt":
-            case "BreakStmt":
-            case "Param":
-            case "IdentTy":
-            case "PtrTy":
-            case "PtrMutTy":
-            case "ArrayTy":
-            case "SliceTy":
-                throw new Error(`node '${k.tag}' not an expression`);
             case "IdentExpr": {
                 const sym = this.syms.get(expr);
                 if (sym.tag === "Fn") {
@@ -453,12 +443,7 @@ class TypeChecker {
                     : null;
                 if (sym?.tag === "Builtin") {
                     if (sym.id === "len") {
-                        checkArgs(
-                            Ty.create("Fn", {
-                                params: [Ty.Any],
-                                retTy: Ty.USize,
-                            }).as("Fn"),
-                        );
+                        checkArgs(Ty.Fn([Ty.Any], Ty.USize, null).as("Fn"));
                         return Ty.USize;
                     }
                     if (sym.id === "print") {
@@ -483,8 +468,60 @@ class TypeChecker {
                 }
 
                 const callableTy = calleeTy.callableTy();
-                checkArgs(callableTy);
-                return callableTy.kind.retTy;
+
+                if (callableTy.kind.generics !== null) {
+                    let generics: Ty[];
+                    if (k.generics) {
+                        generics = k.generics.map((ty) => this.ty(ty));
+                        if (
+                            generics.length !== callableTy.kind.generics.length
+                        ) {
+                            this.reporter.error(
+                                expr.loc,
+                                `expected ${callableTy.kind.generics.length} generic type arguments, got ${generics.length}`,
+                            );
+                            this.reporter.abort();
+                        }
+                    } else {
+                        generics = callableTy.kind.generics
+                            .map((_ty) => Ty.Any);
+                    }
+
+                    const newCalleeTy = Ty.Fn(
+                        callableTy.kind.params
+                            .map((ty) =>
+                                ty.is("Generic") ? generics[ty.kind.idx] : ty
+                            ),
+                        callableTy.kind.retTy.is("Generic")
+                            ? generics[callableTy.kind.retTy.kind.idx]
+                            : callableTy.kind.retTy,
+                        null,
+                    ).as("Fn");
+                    this.rewriteTree(k.value, newCalleeTy);
+
+                    checkArgs(
+                        Ty.Fn(
+                            callableTy.kind.params
+                                .map((ty) =>
+                                    ty.is("Generic")
+                                        ? generics[ty.kind.idx]
+                                        : ty
+                                ),
+                            callableTy.kind.retTy.is("Generic")
+                                ? generics[callableTy.kind.retTy.kind.idx]
+                                : callableTy.kind.retTy,
+                            null,
+                        ).as("Fn"),
+                    );
+                    return callableTy.kind.retTy;
+                } else {
+                    if (k.generics) {
+                        this.reporter.error(expr.loc, "no generics expected");
+                        this.reporter.abort();
+                    }
+                    checkArgs(callableTy);
+                    return callableTy.kind.retTy;
+                }
             }
             case "UnaryExpr": {
                 switch (k.op) {
@@ -578,6 +615,25 @@ class TypeChecker {
                 }
                 return Ty.create("Range", {});
             }
+            case "Error":
+            case "File":
+            case "Block":
+            case "ExprStmt":
+            case "AssignStmt":
+            case "FnStmt":
+            case "ReturnStmt":
+            case "LetStmt":
+            case "IfStmt":
+            case "WhileStmt":
+            case "BreakStmt":
+            case "Param":
+            case "IdentTy":
+            case "PtrTy":
+            case "PtrMutTy":
+            case "ArrayTy":
+            case "SliceTy":
+            case "Generic":
+                throw new Error(`node '${k.tag}' not an expression`);
             default:
                 k satisfies never;
                 throw new Error();
@@ -591,28 +647,6 @@ class TypeChecker {
     private checkTy(ty: ast.Node): Ty {
         const k = ty.kind;
         switch (k.tag) {
-            case "Error":
-            case "File":
-            case "Block":
-            case "ExprStmt":
-            case "AssignStmt":
-            case "FnStmt":
-            case "ReturnStmt":
-            case "LetStmt":
-            case "IfStmt":
-            case "WhileStmt":
-            case "BreakStmt":
-            case "Param":
-            case "IdentExpr":
-            case "IntExpr":
-            case "StrExpr":
-            case "ArrayExpr":
-            case "IndexExpr":
-            case "CallExpr":
-            case "UnaryExpr":
-            case "BinaryExpr":
-            case "RangeExpr":
-                throw new Error(`node '${k.tag}' not a type`);
             case "IdentTy": {
                 const sym = this.syms.get(ty);
                 if (sym.tag === "BuiltinTy") {
@@ -647,6 +681,12 @@ class TypeChecker {
                             );
                     }
                 }
+                if (sym.tag === "Generic") {
+                    if (!this.generics) {
+                        throw new Error();
+                    }
+                    return this.generics[sym.idx];
+                }
                 this.reporter.error(ty.loc, `symbol is not a type`);
                 return this.reporter.abort();
             }
@@ -682,6 +722,29 @@ class TypeChecker {
                 const ty = this.ty(k.ty);
                 return Ty.create("Slice", { ty });
             }
+            case "Error":
+            case "File":
+            case "Block":
+            case "ExprStmt":
+            case "AssignStmt":
+            case "FnStmt":
+            case "ReturnStmt":
+            case "LetStmt":
+            case "IfStmt":
+            case "WhileStmt":
+            case "BreakStmt":
+            case "Param":
+            case "IdentExpr":
+            case "IntExpr":
+            case "StrExpr":
+            case "ArrayExpr":
+            case "IndexExpr":
+            case "CallExpr":
+            case "UnaryExpr":
+            case "BinaryExpr":
+            case "RangeExpr":
+            case "Generic":
+                throw new Error(`node '${k.tag}' not a type`);
         }
     }
 
diff --git a/src/front/parse.ts b/src/front/parse.ts
index bc7eacd..95f266c 100644
--- a/src/front/parse.ts
+++ b/src/front/parse.ts
@@ -71,6 +71,7 @@ export class Parser {
         const loc = this.loc();
         this.step();
         const ident = this.mustEat("ident").value;
+        const genericParams = this.parseGenericParams();
         this.mustEat("(");
         const params: ast.Node[] = [];
         if (!this.test(")")) {
@@ -88,7 +89,13 @@ export class Parser {
             retTy = this.parseTy();
         }
         const body = this.parseBlock();
-        return ast.Node.create(loc, "FnStmt", { ident, params, retTy, body });
+        return ast.Node.create(loc, "FnStmt", {
+            ident,
+            genericParams,
+            params,
+            retTy,
+            body,
+        });
     }
 
     parseReturnStmt(): ast.Node {
@@ -259,19 +266,12 @@ export class Parser {
                 const arg = this.parseExpr();
                 this.mustEat("]");
                 expr = ast.Node.create(loc, "IndexExpr", { value: expr, arg });
+            } else if (this.test("::<")) {
+                const generics = this.parseGenericArgs();
+                this.mustEat("(");
+                expr = this.parseCallExprTail(expr, loc, generics);
             } else if (this.eat("(")) {
-                const args: ast.Node[] = [];
-                if (!this.test(")")) {
-                    args.push(this.parseExpr());
-                    while (this.eat(",")) {
-                        if (this.done || this.test(")")) {
-                            break;
-                        }
-                        args.push(this.parseExpr());
-                    }
-                }
-                this.mustEat(")");
-                expr = ast.Node.create(loc, "CallExpr", { value: expr, args });
+                expr = this.parseCallExprTail(expr, loc, null);
             } else {
                 break;
             }
@@ -279,6 +279,29 @@ export class Parser {
         return expr;
     }
 
+    parseCallExprTail(
+        expr: ast.Node,
+        loc: Loc,
+        generics: ast.Node[] | null,
+    ): ast.Node {
+        const args: ast.Node[] = [];
+        if (!this.test(")")) {
+            args.push(this.parseExpr());
+            while (this.eat(",")) {
+                if (this.done || this.test(")")) {
+                    break;
+                }
+                args.push(this.parseExpr());
+            }
+        }
+        this.mustEat(")");
+        return ast.Node.create(loc, "CallExpr", {
+            value: expr,
+            generics,
+            args,
+        });
+    }
+
     parseOperand(): ast.Node {
         const loc = this.loc();
         if (this.test("ident")) {
@@ -361,6 +384,38 @@ export class Parser {
         }
     }
 
+    parseGenericArgs(): ast.Node[] | null {
+        if (!this.eat("::<")) {
+            return null;
+        }
+        const args: ast.Node[] = [];
+        while (!this.done && !this.test("<")) {
+            args.push(this.parseTy());
+            if (!this.eat(",")) {
+                break;
+            }
+        }
+        this.mustEat(">");
+        return args;
+    }
+
+    parseGenericParams(): ast.Node[] | null {
+        if (!this.eat("<")) {
+            return null;
+        }
+        const params: ast.Node[] = [];
+        while (!this.done && !this.test("<")) {
+            const loc = this.loc();
+            const identTok = this.mustEat("ident");
+            params.push(ast.create(loc, "Generic", { ident: identTok.value }));
+            if (!this.eat(",")) {
+                break;
+            }
+        }
+        this.mustEat(">");
+        return params;
+    }
+
     private mustEat(type: string, loc = this.loc()): Tok {
         const tok = this.current;
         if (tok.type !== type) {
@@ -423,7 +478,7 @@ const keywordPattern =
     /^(?:(?:fn)|(?:return)|(?:let)|(?:if)|(?:else)|(?:while)|(?:break)|(?:or)|(?:and)|(?:not)|(?:mut))/;
 
 const operatorPattern2 =
-    /((?:\->)|(?:==)|(?:!=)|(?:<=)|(?:>=)|(?:<<)|(?:>>)|(?:\.\*)|(?:\.\.)|(?:\.\.=)|[\n\(\)\{\}\[\]\,\.\;\:\!\=\<\>\&\^\|\+\-\*\/\%])/g;
+    /((?:\->)|(?:==)|(?:!=)|(?:<=)|(?:>=)|(?:\:\:<)|(?:<<)|(?:>>)|(?:\.\*)|(?:\.\.)|(?:\.\.=)|[\n\(\)\{\}\[\]\,\.\;\:\!\=\<\>\&\^\|\+\-\*\/\%])/g;
 
 export function tokenize(text: string, reporter: FileReporter): Tok[] {
     return new Lexer()
diff --git a/src/front/resolve.ts b/src/front/resolve.ts
index f9cc4bd..50916b3 100644
--- a/src/front/resolve.ts
+++ b/src/front/resolve.ts
@@ -19,6 +19,12 @@ export type Sym =
     | { tag: "Bool"; value: boolean }
     | { tag: "Builtin"; id: string }
     | { tag: "Fn"; stmt: ast.NodeWithKind<"FnStmt"> }
+    | {
+        tag: "Generic";
+        stmt: ast.Node;
+        generic: ast.NodeWithKind<"Generic">;
+        idx: number;
+    }
     | {
         tag: "FnParam";
         stmt: ast.NodeWithKind<"FnStmt">;
@@ -61,6 +67,19 @@ export function resolve(
             if (k.tag === "FnStmt") {
                 ast.assertNodeWithKind(node, "FnStmt");
                 syms = ResolverSyms.forkFrom(syms);
+                if (k.genericParams) {
+                    for (const [idx, param] of k.genericParams?.entries()) {
+                        ast.assertNodeWithKind(param, "Generic");
+                        const sym: Sym = {
+                            tag: "Generic",
+                            stmt: node,
+                            generic: param,
+                            idx,
+                        };
+                        syms.define(param.kind.ident, sym);
+                        resols.set(param.id, sym);
+                    }
+                }
                 for (const [idx, param] of k.params.entries()) {
                     ast.assertNodeWithKind(param, "Param");
                     const sym: Sym = { tag: "FnParam", stmt: node, param, idx };
diff --git a/src/ty.ts b/src/ty.ts
index cb2e143..11e2420 100644
--- a/src/ty.ts
+++ b/src/ty.ts
@@ -48,6 +48,15 @@ export class Ty {
     static Array(ty: Ty, length: number): Ty {
         return this.create("Array", { ty, length });
     }
+    static Fn(params: Ty[], retTy: Ty, generics: Ty[] | null): Ty {
+        return this.create("Fn", { params, retTy, generics });
+    }
+    static Generic(idx: number): Ty {
+        return this.create("Generic", { idx });
+    }
+    static Instance(ty: Ty, args: Ty[]): Ty {
+        return this.create("Instance", { ty, args });
+    }
 
     /** Only used in type checker. */
     static Any = Ty.create("Any", {});
@@ -67,6 +76,9 @@ export class Ty {
     }
 
     private internHash(): string {
+        if (this.is("FnStmt")) {
+            return JSON.stringify({ ...this.kind, stmt: this.kind.stmt.id });
+        }
         return JSON.stringify(this.kind);
     }
 
@@ -244,8 +256,10 @@ export type TyKind =
     | { tag: "Array"; ty: Ty; length: number }
     | { tag: "Slice"; ty: Ty }
     | { tag: "Range" }
-    | { tag: "Fn"; params: Ty[]; retTy: Ty }
+    | { tag: "Fn"; params: Ty[]; retTy: Ty; generics: Ty[] | null }
     | { tag: "FnStmt"; ty: Ty; stmt: ast.NodeWithKind<"FnStmt"> }
+    | { tag: "Generic"; idx: number }
+    | { tag: "Instance"; ty: Ty; args: Ty[] }
     | { tag: "Any" | "AnyInt" }
     | { tag: "AnyIndexable"; ty: Ty }
     | { tag: "AnyCallable"; ty: Ty }