Cost: most events $5-$25 (some free for educators and students)

What to expect: The 2008 festival theme is "Thinking Big," so look for lectures, exhibitions, screenings and concerts exploring the full scale of human ambition all around the city.

Why to go: There's something for every interest, from talks from economist Jeffrey Sachs and Teach for America founder Wendy Kopp to Michael Miles and Corky Siegal's musical tribute to the American railroads. Visit the comprehensive website to create a festival itinerary and buy tickets.