This book is based on the author's experience with calculations involving polynomial splines. It presents those parts of the theory that are especially useful in calculations and stresses the representation of splines as weighted sums of B-splines. This revised edition has been typeset, and all figures have been redrawn. In a major change, the B-spline theory is now developed directly from the recurrence relations without recourse to divided differences. Almost all formal statements are now provided with proofs, and many minor changes have been made throughout, including the correction of errors.