The main objectives of this book are: 1. To understand the different mud system to be run in the field; 2. To be able to know how to trouble-shoot the associated mud problems; 3. To be able to know how to apply the basic material balance equations in determine the quantity of drilling chemicals, water or oil to be applied; 4. To be able to know the criteria to be considered in mud type selection; 5. To understand the applicable field mechanical solids control; 6. To know different field applicable drilling chemicals; This book introduces the real field situation of the drilling fluids application. The materials presented here are aimed primarily at students of Petroleum Engineering, Chemical Engineering, Geologist, and Chemists, who will most likely have occasion to be Mud Engineers. The fundamental concepts of the Drilling Fluids are presented here in a way that can easily be understood.