There is a short introduction by Mikhalkin: http://arxiv.org/abs/0709.1049 expanded in more detail in this book: http://www.math.toronto.edu/mikha/book.pdf The <a href="http://www.amazon.com/Tropical-Algebraic-Geometry-Oberwolfach-Seminars/dp/303460047X/ref=sr_1_3?ie=UTF8&s=books&qid=1257422793&sr=8-3">Oberwolfach lecture notes</a> by Itenberg, Mikhalkin and Shustin are also nice.