The key events and conditions that helped form and direct the evolution of the United States National Park System are presented in this publication. Information is organized into three sections. Part 1 is a brief introduction calling attention to the complexity of the National Park System's origins and designations. Part 2, the main body of the book, provides an historical review of the conditions and factors influencing the beginnings of the system through 1984. A chronological listing of significant events and park system additions is provided for each time era discussed. Part 3, an appendix, contains a series of maps which illustrate growth patterns within the system and indicate the current status of the park system. A listing of 30 properties that are affiliated with but are not officially in the National Park System is also included. (ML)