This book will helpful to researcher and students to understand the importance of genetic variability. Before the planning of any breeding programme for genetic improvement, the assessment of genetic variability available in germplasm lines and relationship between characters are necessary step. Selection is also effective when there is genetic variability among the individuals in a population. Hence, insight into the magnitude of genetic variability present in a population is of paramount importance to a plant breeder for stating a judicious breeding programme. Knowledge of heritability and genetic advance of the character indicates the scope for the improvement through selection. Heritability estimates along with genetic advance are normally more helpful in predicting the gain under selection.