The scope of improvement of any crop depends upon the magnitude of genetic variability present in the available germplasm. Greater the variability in the available germplasm better would be the chances of selecting superior genotypes. This book aims at providing the basic knowledge to the researchers for carraying out the various breeding programmes on cucumber improvement. The information has been given regarding nature & extent of variability, heritability, genetic advance & genetic gain to have guidelines for selection of desirable traits. Similarly, correlation coefficients along with path analysis have been worked out for yield & other important horticultural traits to select superior genotypes to strengthen ongoing breeding programmes on cucumber. Existence of diversity among the genotypes was also assessed by the considerable amount of variation in cluster means for different characters. Moreover, contribution of different characters towards the divergence has also been worked out to give the more emphasis on the characters contributing greater to the divergence, hence making better opportunities for effective selection & choice of parents in hybridization programmes.