Gingival crevicular fluid (GCF) is defined as the tissue fluid that seeps through the crevicular and junctional epithelium. Many studies on gingival crevicular fluid extend over a period of about 50 years, however its presence is known since 19th century. With so much research now available, it is obvious that GCF provides a unique window for analysis of periodontal condition. The book aims to discuss the clinical significance of GCF, its constituents & methods of collection & processing. The author hopes to guide the readers to understand the role of GCF influencing periodontal health status.