This unit concentrates on three broad topics that are central to the field of cognitive psychology thinking, reasoning and problem solving. The unit begins with elements which obstruct thinking focusing on the importance of the mental images and concepts in our understanding of interactions of the world. Due mention of tools of thinking and various types of thinking has been made. Topics on development of correct thinking, thinking in relation to language and communication and guidelines to nurses have also been adequately covered. The author has examined the scientific methods of problem solving and emphasized the factors affecting problem solving. The unit concludes with role of creativity and critical thinking in problem solving and nursing implications.