This is a book about renal cysts and cystic kidneys. Its contributors have created a resource of current information in a field that once aroused only curiosity, but that now stands at the leading edge of molecular nephrology. Its authorship includes 'oldtimers', who bring the wisdom of experience, and 'newcomers', whose presence attests to the contributions made by the investigative and technological advances of the past decade. Its text is organized to carry the reader from renal cyst to cystic renal disease. Each of its chapters defines or explores a challenge or an advance. Cells that line renal cysts are diverse in structure, type, and perhaps function. The cysts themselves lie within an interstitium that is not normal and may influence cyst development and growth. Experimental analogs of human disease offer increasing opportunities to basic researchers to examine, in sequence and under controlled circumstances, those events that favor nephron dilation, cyst growth and ultimate renal failure.