This book is based on cognitive flexibility in bilingual and multilingual population. Language is one factor that helps constantly to activate and strengthen the inhibitory system. Being fluent in two or more languages influences the cognitive flexibility. This study was determined to understand the difference in cognitive flexibility in bilingual and multilingual population. Person fluent in two languages is sufficient to enjoy the benefits in cognitive flexibility. It is advisable to encourage children to grow in bilingual environment. Although there are studies stating that being bilingual will influence the cognitive flexibility, there is no significant difference in cognitive flexibility in both the population. There are various implications of this study in the intervention of Speech and language disordered population.