diff --git a/c_src/proto_command.c b/c_src/proto_command.c
index 1ad6015..c298a35 100644
--- a/c_src/proto_command.c
+++ b/c_src/proto_command.c
@@ -37,6 +37,7 @@
 #define OPT_GROUP     0x47 // getgrnam()
 #define OPT_CWD       0x43
 #define OPT_ARGV0     0x30
+#define OPT_ENV       0x45
 
 //----------------------------------------------------------------------------
 
@@ -106,12 +107,18 @@ void free_command(struct comm_t *comm)
     comm->exec_opts.argv = NULL;
   }
 
-  // TODO: comm->exec_opts.envp, once it's added
-
   if (comm->exec_opts.cwd != NULL) {
     free(comm->exec_opts.cwd);
     comm->exec_opts.cwd = NULL;
   }
+
+  if (comm->exec_opts.env != NULL) {
+    char **ptr;
+    for (ptr = comm->exec_opts.env; *ptr != NULL; ++ptr)
+      free(*ptr);
+    free(comm->exec_opts.env);
+    comm->exec_opts.env = NULL;
+  }
 }
 
 //----------------------------------------------------------------------------
@@ -203,6 +210,16 @@ int get_group_gid(char *group, gid_t *gid)
   return 0;
 }
 
+static
+void free_env(struct comm_t *comm) {
+  char **env;
+  env = comm->exec_opts.env;
+  while (*env != NULL)
+    free(*env++);
+  free(comm->exec_opts.env);
+  comm->exec_opts.env = NULL;
+}
+
 //----------------------------------------------------------------------------
 
 static
@@ -257,11 +274,10 @@ int parse_exec_command(unsigned char *data, size_t size, struct comm_t *comm)
       return ERR_PARSE;
   }
 
-  // TODO: list of env vars to set
-  // TODO: list of env vars to clear
-
   char *argv0;
   char *ugname;
+  size_t items;
+  char **env_set;
   while (read_at < size) {
     switch (data[read_at++]) {
       // numeric options
@@ -335,6 +351,22 @@ int parse_exec_command(unsigned char *data, size_t size, struct comm_t *comm)
           free(comm->exec_opts.argv[0]);
         comm->exec_opts.argv[0] = argv0;
       break;
+      case OPT_ENV:
+        if (comm->exec_opts.env != NULL)
+          free_env(comm);
+        if (size - read_at < 2)
+          return ERR_PARSE;
+        items = unpack16(data + read_at);
+        read_at += 2;
+        comm->exec_opts.env = env_set = calloc(items, sizeof(char *));
+        while(items-- > 0) {
+          if ((*env_set = parse_nonempty_string(data, size, &read_at)) == NULL) {
+            free_env(comm);
+            return ERR_PARSE;
+          }
+          env_set += 1;
+        }
+      break;
 
       default:
         // unrecognized option tag
diff --git a/c_src/proto_command.h b/c_src/proto_command.h
index d845a08..0611335 100644
--- a/c_src/proto_command.h
+++ b/c_src/proto_command.h
@@ -23,8 +23,7 @@ struct comm_t {
       char *command;
       char **argv;
       char *cwd;
-      // TODO: struct { char *name; char *value } *env_set;
-      // TODO: char **env_clear;
+      char **env;
       unsigned int termsig;
       uint64_t sigmask; // ignored signals
       // modes:
diff --git a/c_src/supervisor_loop.c b/c_src/supervisor_loop.c
index 5af19a9..6990452 100644
--- a/c_src/supervisor_loop.c
+++ b/c_src/supervisor_loop.c
@@ -2,6 +2,7 @@
 
 #include <string.h>
 #include <stdio.h> // snprintf()
+#include <stdlib.h>
 
 #include <unistd.h>
 #include <sys/types.h>
@@ -679,8 +680,6 @@ int child_spawn(struct comm_t *cmd, child_t *child, void *buffer, int *fds)
     }
   }
 
-  // TODO: set environment
-
   struct sigaction ignore_action;
   memset(&ignore_action, 0, sizeof(ignore_action));
   ignore_action.sa_handler = SIG_IGN;
@@ -689,7 +688,7 @@ int child_spawn(struct comm_t *cmd, child_t *child, void *buffer, int *fds)
     if ((cmd->exec_opts.sigmask & (((uint64_t)1) << (sig - 1))) != 0)
       sigaction(sig, &ignore_action, NULL);
 
-  execve(cmd->exec_opts.command, cmd->exec_opts.argv, NULL);
+  execve(cmd->exec_opts.command, cmd->exec_opts.argv, cmd->exec_opts.env);
   // if we got here, exec() must have failed
   int error[2] = { STAGE_EXEC, errno };
   send(fds_confirm[WRITE_END], error, sizeof(error), MSG_NOSIGNAL);
diff --git a/src/subproc.erl b/src/subproc.erl
index cc2e05a..0fd2c8f 100644
--- a/src/subproc.erl
+++ b/src/subproc.erl
@@ -75,6 +75,8 @@
                      | {user, uid() | string()}
                      | {group, gid() | string()}
                      | {cd, file:filename()}
+                     | {environ, map()}
+                     | {environ_pass, [string()]}
                      | {argv0, file:filename()}.
 %% Options controlling how the subprocess is executed.
 %%
@@ -109,6 +111,10 @@
 %%       root rights</li>
 %%   <li>`{cd,_}' -- when set, the subprocess will be spawned in specified
 %%       directory</li>
+%%   <li>`{environ,_}' -- set environment variables for the subprocess.
+%%       Overrides `environ_pass'</li>
+%%   <li>`{environ_pass,_}' -- list of environment variables in the current
+%%       environment to pass through to the subprocess</li>
 %%   <li>`{argv0,_}' -- when set, process name (sometimes called `argv[0]' or
 %%       `$0') will be set to this value</li>
 %% </ul>
diff --git a/src/subproc_master_driver.erl b/src/subproc_master_driver.erl
index c8a80c5..6b2f9d7 100644
--- a/src/subproc_master_driver.erl
+++ b/src/subproc_master_driver.erl
@@ -217,6 +217,8 @@ close(Port) ->
                | {user, uid() | user()}
                | {group, gid() | group()}
                | {cd, file:filename()}
+               | {environ, map()}
+               | {environ_pass, [string()]}
                | {argv0, file:filename()},
        STDIO :: {bidir, FDRW} | {in, FDR} | {out, FDW} | {in_out, {FDR, FDW}},
        FDRW :: subproc:os_fd(),
@@ -551,6 +553,8 @@ build_exec_request(Command, Args, Options) ->
   group :: undefined | gid() | group(),
   nice  :: undefined | integer(),
   cwd   :: undefined | file:filename(),
+  environ :: undefined | map(),
+  environ_pass :: undefined | [string()],
   argv0 :: undefined | file:filename()
 }).
 
@@ -614,6 +618,10 @@ exec_option({group, Group}, Opts) when is_integer(Group); is_list(Group) ->
   Opts#exec{group = Group};
 exec_option({cd, Dir}, Opts) when is_list(Dir) ->
   Opts#exec{cwd = Dir};
+exec_option({environ, Env}, Opts) when is_map(Env) ->
+  Opts#exec{environ = Env};
+exec_option({environ_pass, Vars}, Opts) when is_list(Vars) ->
+  Opts#exec{environ_pass = Vars};
 exec_option({argv0, Name}, Opts) when is_list(Name) ->
   Opts#exec{argv0 = Name}.
 
@@ -642,6 +650,8 @@ is_option({nice, _})  -> true;
 is_option({user, _})  -> true;
 is_option({group, _}) -> true;
 is_option({cd, _})    -> true;
+is_option({environ, _}) -> true;
+is_option({environ_pass, _}) -> true;
 is_option({argv0, _}) -> true;
 is_option(_Value) -> false.
 
@@ -718,6 +728,7 @@ build_exec_options(Opts = #exec{}) ->
   end,
   SigIgnMask = make_signal_mask(Opts#exec.ignore_signals, 0),
   OptSigIgn = <<16#73:8, SigIgnMask:64>>,
+  OptEnv = build_environment_variables(Opts#exec.environ, Opts#exec.environ_pass),
   OptNice = case Opts of
     #exec{nice = undefined} -> [];
     #exec{nice = Nice} -> <<16#70:8, Nice:8>>
@@ -741,7 +752,7 @@ build_exec_options(Opts = #exec{}) ->
     #exec{argv0 = Name} -> pack_tagged_string(16#30, Name)
   end,
   _Result = [
-    OptTermSig, OptSigIgn, OptCwd, OptUser, OptGroup, OptNice, OptArgv0
+    OptTermSig, OptSigIgn, OptCwd, OptUser, OptGroup, OptNice, OptEnv, OptArgv0
   ].
 
 %% @doc Make a signal mask from list of signals (names and/or numbers).
@@ -763,6 +774,29 @@ make_signal_mask([SigName | Rest], Mask) when is_atom(SigName) ->
 make_signal_mask(_SignalList, _Mask) ->
   erlang:error(bad_signal).
 
+%% @doc Build the list of environment variables & values to use
+
+-spec build_environment_variables(undefined | map(), undefined | [iolist()]) ->
+   iolist().
+
+build_environment_variables(undefined, Pass) ->
+  build_environment_variables(#{}, Pass);
+build_environment_variables(Set, undefined) ->
+  build_environment_variables(Set, []);
+build_environment_variables(SetVars, Pass) ->
+  PassVars0 = [{Var, os:getenv(Var)} || Var <- Pass],
+  PassVars1 = [VarDef || {_, Value} = VarDef <- PassVars0, Value =/= false],
+  PassVars = maps:from_list(PassVars1),
+  AllVars = maps:merge(PassVars, SetVars),
+
+  KVs = maps:to_list(AllVars),
+  Strings = [pack_string([K, "=", V]) || {K, V} <- KVs],
+  case Strings of
+    [] -> [];
+    Data ->
+      [<<16#45:8>>, <<(length(Strings)):16>>, Strings]
+  end.
+
 %% }}}
 %%----------------------------------------------------------
 %% string packing {{{