Derivatives tell how a function is changing. Integrals construct the function from its changes. Calculus is the starting point for science and engineering and economics and understanding.

Published in 1991 by Wellesley-Cambridge Press, (hard copies are available for purchase) the book is a useful resource for educators and self-learners alike. It is well organized, covers single variable and multivariable calculus in depth, and is rich with applications. There is also an online Instructor's Manual and a student Study Guide at MIT Open Courseware.