Does the IPython Notebook have "initialization cells"?

When I open a saved IPython Notebook, I need to evaluate all the cells with imports, function definitions etc. to continue working on the session. It is convenient to click Cell > Run All to do this. But what If I do not want to re-evaluate all calculations? Do I need to pick the cells to evaluate by hand each time?

For this problem, Mathematica has the concept of "initialization cells". You can mark some cells in the notebook as initialization cell, and then perform "evaluate initialization cells" after opening the notebook.

Does the IPython Notebook have a similar solution?