For experienced programmers, the clearest introduction to Common Lisp is the first few chapters of "Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp" by Peter Norvig. His writing style is exceptional. Not quite so clear, but also not too dense, is "ANSI Common Lisp" by Paul Graham. Peter Seibel's "Practical Common Lisp" is dense (words per page), but is good for a "now I know a little Lisp, what can I do with it" book to read second. Winston's "Lisp (3rd)" goes from an extremely basic intro to heavy-duty AI without building up to it. But you can get it cheap, so it is worth it for a beginning reference.<p>As a sidenote, when you first look into Lisp, you hear a lot of kvetching and mocking about parentheses. And indeed, there is a point in the learning curve where you get confused about the proper numbers of parentheses for certain kinds of expressions (so-called 'special forms'). And you see Lisp apologists countering that it's not the parentheses that matter; rather the indentation is what helps you understand the code.<p>In my experience, what happens is that as you become familiar with these 'special forms', you learn to recognize the visual patterns of indentation and parentheses that are particular to each of these expressions. And once you write a number of them yourself, grokking the code of others is no problem. And as in all languages, a decent editor and syntax coloring is helpful.