diff --git a/Makefile.am b/Makefile.am
index 17eac4f..eaca651 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -37,6 +37,7 @@ endif # HAVE_GENHTML
 test-list: ; @echo $(TESTS)
 
 MODULES =                                       \
+  geesh/environment.scm                         \
   geesh/lexer.scm                               \
   geesh/parser.scm                              \
   geesh/repl.scm
@@ -45,6 +46,7 @@ bin_SCRIPTS =                                   \
   scripts/geesh
 
 TESTS =                                         \
+  tests/environment.scm                         \
   tests/lexer.scm                               \
   tests/parser.scm                              \
   tests/repl.scm
diff --git a/geesh/environment.scm b/geesh/environment.scm
new file mode 100644
index 0000000..6614733
--- /dev/null
+++ b/geesh/environment.scm
@@ -0,0 +1,53 @@
+;;; The Geesh Shell Interpreter
+;;; Copyright 2018 Timothy Sample <samplet@ngyro.com>
+;;;
+;;; This file is part of Geesh.
+;;;
+;;; Geesh is free software: you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation, either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; Geesh is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Geesh.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (geesh environment)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-9)
+  #:export (<environment>
+            make-environment
+            environment?
+            var-ref
+            set-var!))
+
+;;; Commentary:
+;;;
+;;; This module contains data structures and functions for the
+;;; environment of the Shell language.
+;;;
+;;; Code:
+
+(define-record-type <environment>
+  (%make-environment vars)
+  environment?
+  (vars environment-vars set-environment-vars!))
+
+(define (make-environment vars)
+  ;; In order to insure that each pair in the 'vars' alist is mutable,
+  ;; we copy each one into a new list.
+  (%make-environment (map (match-lambda
+                            ((key . val) (cons key val)))
+                          vars)))
+
+(define (var-ref env name)
+  (assoc-ref (environment-vars env) name))
+
+(define (set-var! env name val)
+  (set-environment-vars! env (acons name val
+                                    (environment-vars env))))
+
diff --git a/tests/environment.scm b/tests/environment.scm
new file mode 100644
index 0000000..147ecb0
--- /dev/null
+++ b/tests/environment.scm
@@ -0,0 +1,56 @@
+;;; The Geesh Shell Interpreter
+;;; Copyright 2018 Timothy Sample <samplet@ngyro.com>
+;;;
+;;; This file is part of Geesh.
+;;;
+;;; Geesh is free software: you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation, either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; Geesh is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Geesh.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (test-environment)
+  #:use-module (geesh environment)
+  #:use-module (srfi srfi-64)
+  #:use-module (tests automake))
+
+;;; Commentary:
+;;;
+;;; Tests for the environment module.
+;;;
+;;; Code:
+
+(test-begin "environment")
+
+;;;
+;;; Variables.
+;;;
+
+(test-equal "Stores existing variables"
+  "bar"
+  (let ((env (make-environment '(("FOO" . "bar")))))
+    (var-ref env "FOO")))
+
+(test-equal "Stores new variables"
+  "bar"
+  (let ((env (make-environment '())))
+    (set-var! env "FOO" "bar")
+    (var-ref env "FOO")))
+
+(test-equal "Updates variables"
+  "baz"
+  (let ((env (make-environment '(("FOO" . "bar")))))
+    (set-var! env "FOO" "baz")
+    (var-ref env "FOO")))
+
+(test-equal "Returns '#f' for unset variables"
+  #f
+  (let ((env (make-environment '())))
+    (var-ref env "FOO")))