The basic version of D&D, takes you all the way up to 3rd level. If you buy this book, definitely consider getting the Expert book as well (hence the name B/X or Basic/Expert). This book originally was meant to be an introduction into AD&D, however it was so successful that TSR decided to give "basic D&D" its own product line. Overall a great purchase if you're into OSR.
[5 of 5 Stars!]