diff --git a/plugin.go b/plugin.go
index 46fd1a7..6d5b730 100644
--- a/plugin.go
+++ b/plugin.go
@@ -18,7 +18,7 @@ type Plugin interface {
 	SetRoutes(group *echo.Group)
 	// Inject is called prior to rendering a template. It can extend the
 	// template data by setting new items in the Extra map.
-	Inject(name string, data interface{}) error
+	Inject(name string, data RenderData) error
 	// Close is called when the plugin is unloaded.
 	Close() error
 }
diff --git a/plugin_go.go b/plugin_go.go
index 43e9aea..407363c 100644
--- a/plugin_go.go
+++ b/plugin_go.go
@@ -40,7 +40,7 @@ func (p *goPlugin) SetRoutes(group *echo.Group) {
 	group.Static("/plugins/"+p.p.Name+"/assets", pluginDir+"/"+p.p.Name+"/public/assets")
 }
 
-func (p *goPlugin) Inject(name string, data interface{}) error {
+func (p *goPlugin) Inject(name string, data RenderData) error {
 	if f, ok := p.p.injectFuncs["*"]; ok {
 		if err := f(data); err != nil {
 			return err
@@ -114,7 +114,7 @@ func (p *GoPlugin) TemplateFuncs(funcs template.FuncMap) {
 }
 
 // InjectFunc is a function that injects data prior to rendering a template.
-type InjectFunc func(data interface{}) error
+type InjectFunc func(data RenderData) error
 
 // Inject registers a function to execute prior to rendering a template. The
 // special name "*" matches any template.
diff --git a/plugin_lua.go b/plugin_lua.go
index 638f17c..816c7f1 100644
--- a/plugin_lua.go
+++ b/plugin_lua.go
@@ -68,7 +68,7 @@ func (p *luaPlugin) setRoute(l *lua.LState) int {
 	return 0
 }
 
-func (p *luaPlugin) inject(name string, data interface{}) error {
+func (p *luaPlugin) inject(name string, data RenderData) error {
 	f, ok := p.renderCallbacks[name]
 	if !ok {
 		return nil
@@ -86,7 +86,7 @@ func (p *luaPlugin) inject(name string, data interface{}) error {
 	return nil
 }
 
-func (p *luaPlugin) Inject(name string, data interface{}) error {
+func (p *luaPlugin) Inject(name string, data RenderData) error {
 	if err := p.inject("*", data); err != nil {
 		return err
 	}
diff --git a/plugins/base/routes.go b/plugins/base/routes.go
index fe3e946..f3f196a 100644
--- a/plugins/base/routes.go
+++ b/plugins/base/routes.go
@@ -116,12 +116,12 @@ func handleGetMailbox(ectx echo.Context) error {
 
 	return ctx.Render(http.StatusOK, "mailbox.html", &MailboxRenderData{
 		BaseRenderData: *koushin.NewBaseRenderData(ctx),
-		Mailbox:    mbox,
-		Mailboxes:  mailboxes,
-		Messages:   msgs,
-		PrevPage:   prevPage,
-		NextPage:   nextPage,
-		Query:      query,
+		Mailbox:        mbox,
+		Mailboxes:      mailboxes,
+		Messages:       msgs,
+		PrevPage:       prevPage,
+		NextPage:       nextPage,
+		Query:          query,
 	})
 }
 
@@ -239,14 +239,14 @@ func handleGetPart(ctx *koushin.Context, raw bool) error {
 	}
 
 	return ctx.Render(http.StatusOK, "message.html", &MessageRenderData{
-		BaseRenderData:  *koushin.NewBaseRenderData(ctx),
-		Mailboxes:   mailboxes,
-		Mailbox:     mbox,
-		Message:     msg,
-		Body:        body,
-		PartPath:    partPathString,
-		MailboxPage: int(mbox.Messages-msg.SeqNum) / messagesPerPage,
-		Flags:       flags,
+		BaseRenderData: *koushin.NewBaseRenderData(ctx),
+		Mailboxes:      mailboxes,
+		Mailbox:        mbox,
+		Message:        msg,
+		Body:           body,
+		PartPath:       partPathString,
+		MailboxPage:    int(mbox.Messages-msg.SeqNum) / messagesPerPage,
+		Flags:          flags,
 	})
 }
 
@@ -354,7 +354,7 @@ func handleCompose(ectx echo.Context) error {
 
 	return ctx.Render(http.StatusOK, "compose.html", &ComposeRenderData{
 		BaseRenderData: *koushin.NewBaseRenderData(ctx),
-		Message:    &msg,
+		Message:        &msg,
 	})
 }
 
diff --git a/template.go b/template.go
index 379b6d5..6286e08 100644
--- a/template.go
+++ b/template.go
@@ -20,18 +20,48 @@ type GlobalRenderData struct {
 	Username string
 	// TODO: list of mailboxes
 
-	// Additional plugin-specific data
+	// additional plugin-specific data
 	Extra map[string]interface{}
 }
 
 // BaseRenderData is the base type for templates. It should be extended with
-// new template-specific fields.
+// additional template-specific fields:
+//
+//     type MyRenderData struct {
+//         BaseRenderData
+//         // add additional fields here
+//     }
 type BaseRenderData struct {
-	Global GlobalRenderData
-	// Additional plugin-specific data
+	GlobalData GlobalRenderData
+	// additional plugin-specific data
 	Extra map[string]interface{}
 }
 
+// Global implements RenderData.
+func (brd *BaseRenderData) Global() *GlobalRenderData {
+	return &brd.GlobalData
+}
+
+// RenderData is implemented by template data structs. It can be used to inject
+// additional data to all templates.
+type RenderData interface {
+	// GlobalData returns a pointer to the global render data.
+	Global() *GlobalRenderData
+}
+
+// NewBaseRenderData initializes a new BaseRenderData.
+//
+// It can be used by routes to pre-fill the base data:
+//
+//     type MyRenderData struct {
+//         BaseRenderData
+//         // add additional fields here
+//     }
+//
+//     data := &MyRenderData{
+//         BaseRenderData: *koushin.NewBaseRenderData(ctx),
+//         // other fields...
+//     }
 func NewBaseRenderData(ctx *Context) *BaseRenderData {
 	global := GlobalRenderData{Extra: make(map[string]interface{})}
 
@@ -41,8 +71,8 @@ func NewBaseRenderData(ctx *Context) *BaseRenderData {
 	}
 
 	return &BaseRenderData{
-		Global: global,
-		Extra:  make(map[string]interface{}),
+		GlobalData: global,
+		Extra:      make(map[string]interface{}),
 	}
 }
 
@@ -57,7 +87,7 @@ func (r *renderer) Render(w io.Writer, name string, data interface{}, ectx echo.
 	ctx := ectx.Get("context").(*Context)
 
 	for _, plugin := range ctx.Server.Plugins {
-		if err := plugin.Inject(name, data); err != nil {
+		if err := plugin.Inject(name, data.(RenderData)); err != nil {
 			return fmt.Errorf("failed to run plugin '%v': %v", plugin.Name(), err)
 		}
 	}