The Science of plant physiology is connected to the material and energy exchange, growth and development, as well as movement of plant. The basic knowledge of plant physiology is necessary for experts in agriculture and other disciplines of plant science. Being one of the key subjects of basic sciences, plant physiology is taught to the students across all the disciplines of plant sciences including agriculture. The purpose of this book is to present precise information about the fundamentals terms and mechanisms of plant physiology in a comprehensible manner for the students, researchers and teachers engaged in agriculture and associated disciplines. The overall contents of this book are divided into 20 different chapters. In this book the basic understanding about the cell and tissue system is described. Basic concepts of solution, suspension and colloidal system are elucidated. Notions are provided about the soil and soil water available to the plants. Principles of water movement, plant water absorption and translocation, and transpiration and crop water use are put in plain words. The basic concepts of plant stress physiology are complemented with the presentation of physiological mechanisms against different environmental stresses. Concept and theories of nutrient essentiality, and their uptake and transport are explained. Concepts and terminologies related to plant growth and growth regulators are clarified. Fundamental terms and principles about biological catalysts (enzymes) are defined and explained precisely. Critical explanation of the terms related to the vital physiological processes like photosynthesis and respiration are provided. Terminologies related to carbohydrate, nitrogen, protein, lipid and fat metabolism are expounded. Glossary of plant movement and biological clock, photoperiodism and vernalization, and seed dormancy and germination are presented in a trouble-free mode. In addition, a concluding chapter is presented as miscellaneous terms used in sister disciplines of agriculture. We are sure that the information provided in this book will be quite useful for the students of agriculture and plant sciences at all levels. The book will also be helpful for those who are preparing for various competitive examinations like UG and PG entrance exams in agriculture and medical sciences, JRF/ SRF, NET, ARS examination of ICAR/ UGC/ CSIR, etc. Finally, we request the beloved students and other readers of this book to inform us about the constructive suggestions and criticism for further improvement of the book.