diff --git a/src/libratbag-private.h b/src/libratbag-private.h
index 8cecdbb3..b152b504 100644
--- a/src/libratbag-private.h
+++ b/src/libratbag-private.h
@@ -52,6 +52,8 @@ struct ratbag {
 
 struct ratbag_device {
 	char *name;
+	void *userdata;
+
 	struct udev_device *udev_device;
 	struct udev_device *udev_hidraw;
 	int hidraw_fd;
@@ -178,6 +180,8 @@ struct ratbag_driver {
 
 struct ratbag_profile {
 	int refcount;
+	void *userdata;
+
 	struct list link;
 	unsigned index;
 	struct ratbag_device *device;
@@ -218,6 +222,7 @@ struct ratbag_button_action {
 
 struct ratbag_button {
 	int refcount;
+	void *userdata;
 	struct list link;
 	struct ratbag_profile *profile;
 	unsigned index;
diff --git a/src/libratbag.c b/src/libratbag.c
index 42aec6db..cc3c730b 100644
--- a/src/libratbag.c
+++ b/src/libratbag.c
@@ -895,3 +895,22 @@ ratbag_button_unref(struct ratbag_button *button)
 
 	return NULL;
 }
+
+
+#define func_userdata(T) \
+LIBRATBAG_EXPORT void \
+T##_set_user_data(struct T *ptr, void *userdata) \
+{ \
+	ptr->userdata = userdata; \
+} \
+\
+LIBRATBAG_EXPORT void * \
+T##_get_user_data(const struct T *ptr) \
+{ \
+	return ptr->userdata; \
+} \
+
+func_userdata(ratbag)
+func_userdata(ratbag_device)
+func_userdata(ratbag_profile)
+func_userdata(ratbag_button)
diff --git a/src/libratbag.h b/src/libratbag.h
index c41ec0cd..4f5daec3 100644
--- a/src/libratbag.h
+++ b/src/libratbag.h
@@ -94,8 +94,6 @@ typedef void (*ratbag_log_handler)(struct ratbag *ratbag,
  *
  * A ratbag context represents one single device. This struct is
  * refcounted, use ratbag_device_ref() and ratbag_device_unref().
- *
- * FIXME: missing: set/get_userdata
  */
 struct ratbag_device;
 
@@ -107,8 +105,6 @@ struct ratbag_device;
  * RATBAG_CAP_SWITCHABLE_PROFILE capability.
  * This struct is refcounted, use ratbag_profile_ref() and
  * ratbag_profile_unref().
- *
- * FIXME: missing: set/get_userdata
  */
 struct ratbag_profile;
 
@@ -120,8 +116,6 @@ struct ratbag_profile;
  *
  * This struct is refcounted, use ratbag_button_ref() and
  * ratbag_button_unref().
- *
- * FIXME: missing: set/get_userdata
  */
 struct ratbag_button;
 
@@ -169,6 +163,34 @@ struct ratbag *
 ratbag_create_context(const struct ratbag_interface *interface,
 			 void *userdata);
 
+/**
+ * @ingroup base
+ *
+ * Set caller-specific data associated with this context. libratbag does
+ * not manage, look at, or modify this data. The caller must ensure the
+ * data is valid.
+ *
+ * Setting userdata overrides the one provided to ratbag_create_context().
+ *
+ * @param ratbag A previously initialized ratbag context
+ * @param userdata Caller-specific data passed to the various callback
+ * interfaces.
+ */
+void
+ratbag_set_user_data(struct ratbag *ratbag, void *userdata);
+
+/**
+ * @ingroup base
+ *
+ * Get the caller-specific data associated with this context, if any.
+ *
+ * @param ratbag A previously initialized ratbag context
+ * @return The caller-specific data previously assigned in
+ * ratbag_create_context (or ratbag_set_user_data()).
+ */
+void*
+ratbag_get_user_data(const struct ratbag *ratbag);
+
 /**
  * @ingroup base
  *
@@ -203,6 +225,32 @@ struct ratbag_device*
 ratbag_device_new_from_udev_device(struct ratbag *ratbag,
 				   struct udev_device *device);
 
+/**
+ * @ingroup device
+ *
+ * Set caller-specific data associated with this device. libratbag does
+ * not manage, look at, or modify this data. The caller must ensure the
+ * data is valid.
+ *
+ * @param device A previously initialized device
+ * @param userdata Caller-specific data passed to the various callback
+ * interfaces.
+ */
+void
+ratbag_device_set_user_data(struct ratbag_device *device, void *userdata);
+
+/**
+ * @ingroup device
+ *
+ * Get the caller-specific data associated with this device, if any.
+ *
+ * @param device A previously initialized ratbag device
+ * @return The caller-specific data previously assigned in
+ * ratbag_device_set_user_data().
+ */
+void*
+ratbag_device_get_user_data(const struct ratbag_device *device);
+
 /**
  * @ingroup device
  *
@@ -285,6 +333,32 @@ ratbag_device_get_num_profiles(struct ratbag_device *ratbag);
 unsigned int
 ratbag_device_get_num_buttons(struct ratbag_device *ratbag);
 
+/**
+ * @ingroup device
+ *
+ * Set caller-specific data associated with this profile. libratbag does
+ * not manage, look at, or modify this data. The caller must ensure the
+ * data is valid.
+ *
+ * @param profile A previously initialized profile
+ * @param userdata Caller-specific data passed to the various callback
+ * interfaces.
+ */
+void
+ratbag_profile_set_user_data(struct ratbag_profile *profile, void *userdata);
+
+/**
+ * @ingroup device
+ *
+ * Get the caller-specific data associated with this profile, if any.
+ *
+ * @param profile A previously initialized ratbag profile
+ * @return The caller-specific data previously assigned in
+ * ratbag_profile_set_user_data().
+ */
+void*
+ratbag_profile_get_user_data(const struct ratbag_profile *profile);
+
 /**
  * @ingroup device
  *
@@ -408,6 +482,32 @@ struct ratbag_button*
 ratbag_profile_get_button_by_index(struct ratbag_profile *profile,
 				   unsigned int index);
 
+/**
+ * @ingroup device
+ *
+ * Set caller-specific data associated with this button. libratbag does
+ * not manage, look at, or modify this data. The caller must ensure the
+ * data is valid.
+ *
+ * @param button A previously initialized button
+ * @param userdata Caller-specific data passed to the various callback
+ * interfaces.
+ */
+void
+ratbag_button_set_user_data(struct ratbag_button *button, void *userdata);
+
+/**
+ * @ingroup device
+ *
+ * Get the caller-specific data associated with this button, if any.
+ *
+ * @param button A previously initialized ratbag button
+ * @return The caller-specific data previously assigned in
+ * ratbag_button_set_user_data().
+ */
+void*
+ratbag_button_get_user_data(const struct ratbag_button *button);
+
 enum ratbag_button_type {
 	RATBAG_BUTTON_TYPE_UNKNOWN = 0,
 
diff --git a/src/libratbag.sym b/src/libratbag.sym
index 43716db0..7f8c4f5d 100644
--- a/src/libratbag.sym
+++ b/src/libratbag.sym
@@ -10,9 +10,11 @@ global:
 	ratbag_button_get_button;
 	ratbag_button_get_key;
 	ratbag_button_get_special;
+	ratbag_button_get_user_data;
 	ratbag_button_set_button;
 	ratbag_button_set_key;
 	ratbag_button_set_special;
+	ratbag_button_set_user_data;
 	ratbag_button_unref;
 	ratbag_device_unref;
 	ratbag_device_get_active_profile;
@@ -20,20 +22,26 @@ global:
 	ratbag_device_get_num_profiles;
 	ratbag_device_get_num_buttons;
 	ratbag_device_get_profile_by_index;
+	ratbag_device_get_user_data;
 	ratbag_device_has_capability;
 	ratbag_device_new_from_udev_device;
 	ratbag_device_ref;
+	ratbag_device_set_user_data;
 	ratbag_device_set_active_profile;
+	ratbag_get_user_data;
 	ratbag_log_get_priority;
 	ratbag_log_set_handler;
 	ratbag_log_set_priority;
 	ratbag_profile_get_button_by_index;
 	ratbag_profile_get_report_rate_hz;
 	ratbag_profile_get_resolution_dpi;
+	ratbag_profile_get_user_data;
 	ratbag_profile_set_resolution_dpi;
+	ratbag_profile_set_user_data;
 	ratbag_profile_ref;
 	ratbag_profile_unref;
 	ratbag_ref;
+	ratbag_set_user_data;
 	ratbag_unref;
 local:
 	*;