Borrowing is quite clearly a component of language growth. As a result, it is a continuous process. Once the words are borrowed, adaptation strategies are applied to allow the borrowed lexicon fit into the phonological and morphological structures of the recipient language. Every language whose speakers have had contact with another or other languages cannot be completely free of borrowed forms. Gĩkũyũ language has had long contact with English and Kiswahili from early last century. As a result, Gĩkũyũ has borrowed a lot from the two languages. This book explores the various phonological and morphological strategies applied by speakers of Gĩ-Gĩchũgũ dialect of Gĩkũyũ language in borrowing words from English and Kiswahili. To do this, the book applies Source-Similarity model, one of the most recent strands of Optimality Theory. This model exploits loanword specific faithfulness constraints that impose maximal similarity between the perceived source form and its corresponding spoken loanword. The book is written with a wide spectrum audience in mind as reference material ranging from High School students, undergraduate and post graduate students.