This is a completely rewritten and expanded version of the successful 1984 book of the same name published by Butterworths. The objective remains the same: to teach students of agriculture and related ecological problems how to express ideas mathematically and solve the resulting mathematical problem. The book is designed to be a textbook, and is suitable for self-study, with exercises and answers. While the level of mathematics is dictated by the problem, the book uses a qualified simplicity. The need of many students to grasp every step of a mathematical model is appreciated and catered for. This book will appeal to graduate students and researchers in agriculture, including crop, environmental, and animal sciences.