PRICES MAY VARY. This book is dedicated to the mathematics of differential operators : gradient; - divergence; - curl. After recalling the most important properties of the concept of derivative of a one-variable function, we introduce the nabla operator, used to describe the three differential operators: gradient, divergence and curl. We discuss characteristics and properties of each operator, showing their formulas with detailed demonstrations. Finally, we consider all the possible mixed products between differential operators, such as the curl of curl of a vector function, showing all the mathematical steps to obtain the final expressions.