diff --git a/lib/scheme/eval.sx b/lib/scheme/eval.sx
index 48a1d208..5af0c24d 100644
--- a/lib/scheme/eval.sx
+++ b/lib/scheme/eval.sx
@@ -568,6 +568,139 @@
          :rules (rest args)
          :env env}))))
 
+;; ── define-library + import (R7RS Phase 8) ─────────────────────
+;;
+;; A library is a tagged value with exports + an env where the body
+;; was evaluated. The global registry maps a string key (joined from
+;; the library-name list) to the library value.
+;;
+;; (define-library NAME EXPR...) where EXPR can be:
+;;   (export NAME ...)
+;;   (import LIB-NAME ...)
+;;   (begin BODY ...)
+;; cond-expand, include, include-library-declarations: deferred.
+;;
+;; (import LIB-NAME ...) at the top level: for each named library,
+;; look up its exports and bind them in the current env.
+
+(define scheme-library-registry {})
+
+(define scm-lib-key
+  (fn (name)
+    (cond
+      ((string? name) name)
+      ((list? name) (scm-join-strings name "/"))
+      (:else (error "library name must be symbol or list")))))
+
+(define scm-join-strings
+  (fn (xs sep)
+    (cond
+      ((or (nil? xs) (= (length xs) 0)) "")
+      ((= (length xs) 1) (first xs))
+      (:else
+        (str (first xs) sep (scm-join-strings (rest xs) sep))))))
+
+(define scm-library?
+  (fn (v)
+    (and (dict? v) (= (get v :scm-tag) :library))))
+
+(define scm-collect-exports
+  (fn (forms acc)
+    (cond
+      ((or (nil? forms) (= (length forms) 0)) acc)
+      (:else
+        (let ((form (first forms)))
+          (cond
+            ((and (list? form) (>= (length form) 1)
+                  (string? (first form)) (= (first form) "export"))
+              (scm-collect-exports (rest forms)
+                                   (scm-list-concat acc (rest form))))
+            (:else (scm-collect-exports (rest forms) acc))))))))
+
+(define scm-run-library-body
+  (fn (forms env)
+    (cond
+      ((or (nil? forms) (= (length forms) 0)) nil)
+      (:else
+        (let ((form (first forms)))
+          (cond
+            ;; export/import declarations: handled separately
+            ((and (list? form) (>= (length form) 1)
+                  (string? (first form))
+                  (or (= (first form) "export")
+                      (= (first form) "import")))
+              (cond
+                ((= (first form) "import")
+                  (begin
+                    (scm-do-import (rest form) env)
+                    (scm-run-library-body (rest forms) env)))
+                (:else (scm-run-library-body (rest forms) env))))
+            ;; begin: evaluate body
+            ((and (list? form) (>= (length form) 1)
+                  (string? (first form)) (= (first form) "begin"))
+              (begin
+                (scheme-eval-body (rest form) env)
+                (scm-run-library-body (rest forms) env)))
+            (:else (scm-run-library-body (rest forms) env))))))))
+
+(define scm-do-import
+  (fn (lib-names env)
+    (cond
+      ((or (nil? lib-names) (= (length lib-names) 0)) nil)
+      (:else
+        (let ((key (scm-lib-key (first lib-names))))
+          (cond
+            ((not (dict-has? scheme-library-registry key))
+              (error (str "import: unknown library: " key)))
+            (:else
+              (begin
+                (let ((lib (get scheme-library-registry key)))
+                  (scm-copy-exports! env
+                                     (get lib :exports)
+                                     (get lib :env)))
+                (scm-do-import (rest lib-names) env)))))))))
+
+(define scm-copy-exports!
+  (fn (target-env exports source-env)
+    (cond
+      ((or (nil? exports) (= (length exports) 0)) nil)
+      (:else
+        (let ((name (first exports)))
+          (cond
+            ((refl-env-has? source-env name)
+              (begin
+                (scheme-env-bind! target-env name
+                                  (refl-env-lookup source-env name))
+                (scm-copy-exports! target-env (rest exports) source-env)))
+            (:else
+              (error (str "import: export not defined: " name)))))))))
+
+(scheme-define-op! "define-library"
+  (fn (args env)
+    (cond
+      ((< (length args) 1)
+        (error "define-library: expects (define-library NAME body...)"))
+      (:else
+        (let ((lib-name (first args))
+              (body (rest args)))
+          (let ((lib-env (scheme-standard-env))
+                (exports (scm-collect-exports body (list)))
+                (key (scm-lib-key lib-name)))
+            (begin
+              (scm-run-library-body body lib-env)
+              (dict-set! scheme-library-registry key
+                         {:scm-tag :library
+                          :name lib-name
+                          :exports exports
+                          :env lib-env})
+              key)))))))
+
+(scheme-define-op! "import"
+  (fn (args env)
+    (begin
+      (scm-do-import args env)
+      nil)))
+
 ;; ── define-record-type (R7RS Phase 9) ──────────────────────────
 ;;
 ;; (define-record-type NAME
diff --git a/lib/scheme/tests/modules.sx b/lib/scheme/tests/modules.sx
new file mode 100644
index 00000000..4dc5d841
--- /dev/null
+++ b/lib/scheme/tests/modules.sx
@@ -0,0 +1,73 @@
+;; lib/scheme/tests/modules.sx — define-library + import.
+
+(define scm-mod-pass 0)
+(define scm-mod-fail 0)
+(define scm-mod-fails (list))
+
+(define
+  scm-mod-test
+  (fn
+    (name actual expected)
+    (if
+      (= actual expected)
+      (set! scm-mod-pass (+ scm-mod-pass 1))
+      (begin
+        (set! scm-mod-fail (+ scm-mod-fail 1))
+        (append! scm-mod-fails {:name name :actual actual :expected expected})))))
+
+(define
+  scm-mod
+  (fn
+    (src)
+    (scheme-eval-program (scheme-parse-all src) (scheme-standard-env))))
+
+;; ── Basic define-library + import ───────────────────────────────
+
+(scm-mod-test
+  "simple lib: sq exported"
+  (scm-mod
+    "(define-library (my math)\n       (export sq)\n       (begin (define (sq x) (* x x))))\n     (import (my math))\n     (sq 5)")
+  25)
+(scm-mod-test
+  "lib: multiple exports"
+  (scm-mod
+    "(define-library (my math)\n       (export sq cube)\n       (begin\n         (define (sq x) (* x x))\n         (define (cube x) (* x x x))))\n     (import (my math))\n     (list (sq 5) (cube 3))")
+  (list 25 27))
+(scm-mod-test
+  "lib: single-symbol name"
+  (scm-mod
+    "(define-library (utils)\n       (export greet)\n       (begin (define (greet name) (string-append \"hi \" name))))\n     (import (utils))\n     (string=? (greet \"world\") \"hi world\")")
+  true)
+
+;; ── Unexported names are not visible ───────────────────────────
+
+(scm-mod-test
+  "lib: private name not exported"
+  (scm-mod
+    "(define-library (my math)\n       (export sq)\n       (begin\n         (define (sq x) (* x x))\n         (define (private-helper x) (+ x 1))))\n     (import (my math))\n     (guard (e (else 'unbound)) private-helper)")
+  "unbound")
+
+;; ── Library calls its own internals ─────────────────────────────
+
+(scm-mod-test
+  "lib: internal calls private fn"
+  (scm-mod
+    "(define-library (my math)\n       (export public-add1)\n       (begin\n         (define (private-inc x) (+ x 1))\n         (define (public-add1 x) (private-inc x))))\n     (import (my math))\n     (public-add1 41)")
+  42)
+
+;; ── Two libs, both imported ────────────────────────────────────
+
+(scm-mod-test
+  "two libs: both imported"
+  (scm-mod
+    "(define-library (a) (export af) (begin (define (af) 1)))\n     (define-library (b) (export bf) (begin (define (bf) 2)))\n     (import (a) (b))\n     (+ (af) (bf))")
+  3)
+
+;; ── Unknown library import errors ──────────────────────────────
+
+(scm-mod-test
+  "import: unknown lib errors"
+  (scm-mod "(guard (e (else 'unknown-lib)) (import (no such lib)))")
+  "unknown-lib")
+
+(define scm-mod-tests-run! (fn () {:total (+ scm-mod-pass scm-mod-fail) :passed scm-mod-pass :failed scm-mod-fail :fails scm-mod-fails}))