The goal is to read the following book: \vskip .1in \noindent ``A first course in String Theory", by Barton Zwiebach. \vskip .1in \noindent In the hands of Witten and other mathematical physicists, string theories (and more generally, the techniques of quantum field theory) have had a gigantic impact on geometry and topology over the last twenty years. Though the genuine physical significance of these subjects is still debatable (many of the mathematically-interesting models are what physicists would call ``toy models") and physicists' methods often lack adequate mathematical foundations, they have a strong internal consistency and lead to numerous surprising mathematical conjectures which could scarcely have been contemplated without this insight. \vskip .1in \noindent We want in our seminar to try to understand the way physicists work. This is actually quite a hard task, because their goals, intuition and language are really different from ours, and require continual translation. (I would sum up the distinction by saying that mathematicians deal mostly in nouns, physicists in verbs.) Zwiebach's book, for an MIT undergraduate physics course, seems to me unusually readable. Its level of mathematical sophistication is not very high, so we will probably be able to worry mostly about the actual physics. Perhaps later on we can try to read some of the rather more advanced book \vskip .1in \noindent ``String theory", by Joseph Polchinski.