This book provides a simplified description of the partial process of photosynthesis at a molecular, organelle, cell and organ levels of organization in plants, which contribute to the complete process. It considers how photophysics and biochemistry determine the physiological characteristics of plants and production of plant dry matter. The text links the fundamentals of light capture by pigment molecules to the generation of high energy organic molecules and their consumption in carbon dioxide, nitrate and sulphate reduction. The mechanisms are related to the structure and function of the leaf and to control of energy and material fluxes. Photosynthesis in leaves is analyzed as the resultant of light activation, biochemical demand, and the supply of CO2. Photosynthetic processes are related to plant environment, sun and shade leaves for example, and C4 and CAM photosynthesis are analyzed as ecophysiological variants of a basic process. Leaf photosynthesis is put into context as one, albeit the major, determinant of productivity of vegetation. Plant productivity is the result of the interaction of many sub-systems, all driven by the primary energy capture. Photosynthesis by the whole plant is to be seen as a series of balanced but dynamic interactions between individual molecular and physiological mechanisms. The text is intended for undergraduate and graduate study in plant biology courses and for non-specialists in other disciplines who wish to understand photosynthetic mechanisms and control. The approach is qualitative, but there is some emphasis on quantitative aspects to encourage progress towards more rigorous analysis of the photosynthetic system, for example by modelling and systems analysis. References are mainly from the secondary or review literature, from which detailed arguments and the primary literature may be obtained.