This book entitled “Effect of GA3 and Ethrel on vigour, flowering and yield of French marigold (T. patula linn.). Gibberellic acid and Ethrel is one of the important growth regulators playing a crucial role in plant life cycle. From its role in germination of seeds to stem elongation, flowering and fruit development, this plant “hormone” is vital to growth and reproduction of plant. In this book described the effect of GA3 and Ethrel on French marigold (Tagetes patula). GA3 at 200 ppm performed well for increasing vigour, fresh weight of flower, flower yield and induced early flowering whereas Ethrel at higher concentration (440 ppm) reduced plant height and increased no. of branches but decreasing the diameter of plant, length of leaf, diameter of flower, fresh weight of flower, yield per plant and per ha. The experiment was carrying at Department of Horticulture, Kulbhaskar Ashram P. G. College, Allahabad during winter season of 2012-2013.In writing certain chapters in this book, this information available for future use of students.