diff --git a/photobooth/StateMachine.py b/photobooth/StateMachine.py
new file mode 100644
index 0000000..45a166c
--- /dev/null
+++ b/photobooth/StateMachine.py
@@ -0,0 +1,351 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+# Photobooth - a flexible photo booth software
+# Copyright (C) 2018  Balthasar Reuter <photobooth at re - web dot eu>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+
+class Context:
+
+    def __init__(self, initial_state):
+
+        super().__init__()
+
+        self.state = initial_state
+
+    @property
+    def state(self):
+
+        return self._state
+
+    @state.setter
+    def state(self, new_state):
+
+        if not isinstance(new_state, State):
+            raise TypeError('new_state must implement State')
+
+    def handleEvent(self, event):
+
+        if not isinstance(event, Event):
+            raise TypeError('event must implement Event')
+
+        if isinstance(event, ErrorEvent):
+            self.state = ErrorState(event.exception, self.state)
+        elif isinstance(event, TeardownEvent):
+            self.state = TeardownState(event.target)
+        else:
+            self.state.handleEvent(event, self)
+
+
+class Event:
+
+    def __init__(self, name):
+
+        super().__init__()
+        self.name = name
+
+    def __str__(self):
+
+        return self.name
+
+    @property
+    def name(self):
+
+        return self._name
+
+    @name.setter
+    def name(self, name):
+
+        if not isinstance(name, str):
+            raise TypeError('name must be a str')
+
+        self._name = name
+
+
+class ErrorEvent(Event):
+
+    def __init__(self, exception):
+
+        super().__init__('Error')
+        self.exception = exception
+
+    def __str__(self):
+
+        return str(self.exception)
+
+    @property
+    def exception(self):
+
+        return self._exception
+
+    @exception.setter
+    def exception(self, exception):
+
+        if not isinstance(exception, Exception):
+            raise TypeError('exception must be derived from Exception')
+
+        self._exception = exception
+
+
+class TeardownEvent(Event):
+
+    EXIT = 0
+    RESTART = 1
+    WELCOME = 2
+
+    def __init__(self, target):
+
+        self._target = target
+        super().__init__('Teardown')
+
+    @property
+    def target(self):
+
+        return self._target
+
+
+class GuiEvent(Event):
+
+    def __init__(self, name):
+
+        super().__init__(name)
+
+
+class GpioEvent(Event):
+
+    def __init__(self, name):
+
+        super().__init__(name)
+
+
+class CameraEvent(Event):
+
+    def __init__(self, name):
+
+        super().__init__(name)
+
+
+class WorkerEvent(Event):
+
+    def __init__(self, name):
+
+        super().__init__(name)
+
+
+class State:
+
+    def __init__(self):
+
+        super().__init__()
+        self.update()
+
+    def update(self):
+
+        pass
+
+    def handleEvent(self, event, context):
+
+        raise NotImplementedError()
+
+
+class ErrorState(State):
+
+    def __init__(self, exception, old_state):
+
+        self.old_state = old_state
+        super().__init__()
+
+    @property
+    def old_state(self):
+
+        return self._old_state
+
+    @old_state.setter
+    def old_state(self, old_state):
+
+        if not isinstance(old_state, State):
+            raise TypeError('old_state must be derived from State')
+
+        self._old_state = old_state
+
+    def handleEvent(self, event, context):
+
+        if isinstance(event, GuiEvent) and event.name == 'retry':
+            context.state = self.old_state
+            context.state.update()
+        elif isinstance(event, GuiEvent) and event.name == 'abort':
+            context.state = TeardownState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class TeardownState(State):
+
+    def __init__(self, target):
+
+        super().__init__()
+
+
+class WelcomeState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if isinstance(event, GuiEvent):
+            if event.name == 'start':
+                context.state = StartupState()
+            elif event.name == 'settings':
+                context.state = SettingsState()
+            elif event.name == 'exit':
+                context.state = TeardownState()
+            else:
+                raise ValueError('Unknown GuiEvent "{}"'.format(event.name))
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class SettingsState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if isinstance(event, GuiEvent) and event.name == 'welcome':
+            context.state = WelcomeState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class StartupState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if isinstance(event, CameraEvent) and event.name == 'ready':
+            context.state = IdleState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class IdleState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if ((isinstance(event, GuiEvent) or isinstance(event, GpioEvent)) and
+           event.name == 'trigger'):
+            context.state = GreeterState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class GreeterState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if ((isinstance(event, GuiEvent) or isinstance(event, GpioEvent)) and
+           event.name == 'countdown'):
+            context.state = CountdownState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class CountdownState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if isinstance(event, GuiEvent) and event.name == 'capture':
+            context.state == CaptureState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class CaptureState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if isinstance(event, CameraEvent) and event.name == 'next':
+            context.state = CountdownState()
+        elif isinstance(event, CameraEvent) and event.name == 'assemble':
+            context.state = AssembleState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class AssembleState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if isinstance(event, CameraEvent) and event.name == 'review':
+            context.state = ReviewState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class ReviewState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if isinstance(event, GuiEvent) and event.name == 'postprocess':
+            context.state == PostprocessState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))
+
+
+class PostprocessState(State):
+
+    def __init__(self):
+
+        super().__init__()
+
+    def handleEvent(self, event, context):
+
+        if ((isinstance(event, GuiEvent) or isinstance(event, GpioEvent)) and
+           event.name == 'idle'):
+            context.state == IdleState()
+        else:
+            raise TypeError('Unknown Event type "{}"'.format(event))