This introduction to psychology is addressed to all those who want to begin a discipline that now has become essential in the formation and practice of many professions. With a clear and readable style, the author explains basic scientific concepts by setting the maximum number of connections to everyday experiences of the reader. In order not to present psychology as a field of only research but also as an applied science, in all the chapters include "Further reading" provide examples of psychological research on the issues. Since the first edition of Keys of psychology in 1979, Dr. Mietzel has continued to revise and update his work. Repeated testing issues are raised wide interest in this book readers in recent years has become a classic in the field of education. Over nine chapters, Mietzel collects current scientific knowledge of almost all fields of psychology of action: human development, perception, learning, problem solving, intelligence, memory, motivation, emotions and stress. Very useful is also the extensive bibliography (provided the Spanish translation if any). For psychology students, psychologists, psychotherapists and anyone interested in psychology.