diff --git a/config.go b/config.go
index c733639..560300e 100644
--- a/config.go
+++ b/config.go
@@ -27,12 +27,13 @@ type Window struct {
 }
 
 type Config struct {
-	Session                   string   `yaml:"session"`
-	Root                      string   `yaml:"root"`
-	BeforeStart               []string `yaml:"before_start"`
-	Stop                      []string `yaml:"stop"`
-	Windows                   []Window `yaml:"windows"`
-	RebalanceWindowsThreshold int      `yaml:"rebalance_panes_after"`
+	Session                   string            `yaml:"session"`
+	Env                       map[string]string `yaml:"env"`
+	Root                      string            `yaml:"root"`
+	BeforeStart               []string          `yaml:"before_start"`
+	Stop                      []string          `yaml:"stop"`
+	Windows                   []Window          `yaml:"windows"`
+	RebalanceWindowsThreshold int               `yaml:"rebalance_panes_after"`
 }
 
 func EditConfig(path string) error {
diff --git a/smug.go b/smug.go
index 2de127c..afa7ab8 100644
--- a/smug.go
+++ b/smug.go
@@ -55,6 +55,17 @@ func (smug Smug) execShellCommands(commands []string, path string) error {
 	return nil
 }
 
+func (smug Smug) setEnvVariables(target string, env map[string]string) error {
+	for key, value := range env {
+		_, err := smug.tmux.SetEnv(target, key, value)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 func (smug Smug) switchOrAttach(target string, attach bool, insideTmuxSession bool) error {
 	if insideTmuxSession && attach {
 		return smug.tmux.SwitchClient(target)
@@ -110,6 +121,11 @@ func (smug Smug) Start(config Config, options Options, context Context) error {
 		if err != nil {
 			return err
 		}
+
+		err = smug.setEnvVariables(config.Session, config.Env)
+		if err != nil {
+			return err
+		}
 	} else if len(windows) == 0 {
 		return smug.switchOrAttach(sessionName, attach, context.InsideTmuxSession)
 	}
diff --git a/tmux.go b/tmux.go
index 449c8c1..e00750f 100644
--- a/tmux.go
+++ b/tmux.go
@@ -105,6 +105,11 @@ func (tmux Tmux) SelectLayout(target string, layoutType string) (string, error)
 	return tmux.commander.Exec(cmd)
 }
 
+func (tmux Tmux) SetEnv(target string, key string, value string) (string, error) {
+	cmd := exec.Command("tmux", "setenv", "-t", target, key, value)
+	return tmux.commander.Exec(cmd)
+}
+
 func (tmux Tmux) StopSession(target string) (string, error) {
 	cmd := exec.Command("tmux", "kill-session", "-t", target)
 	return tmux.commander.Exec(cmd)