The Art of Problem Solving!!!
Cannot recommend highly enough. Comprehensive, rigorous, and well written. Amazing community around them too. Can take you all the way to the IMO, if you want.
Cannot recommend highly enough. Comprehensive, rigorous, and well written. Amazing community around them too. Can take you all the way to the IMO, if you want.
Taken from the description of one of their books:
"The text is structured to inspire the reader to explore and develop new ideas. Each section starts with problems, giving the student a chance to solve them without help before proceeding. The text then includes solutions to these problems, through which algebraic techniques are taught. Important facts and powerful problem solving approaches are highlighted throughout the text. In addition to the instructional material, the book contains well over 1000 problems."