The C Programming Language (sometimes referred to as K&R, or the white bible, or K&R2 for the second edition) is a well-known programming book written by Brian Kernighan and Dennis Ritchie, the latter of whom originally designed and implemented the language (as well as co-designed the Unix operating system with which development of the language was closely intertwined). The book was central to the development and popularization of the C programming language and is still widely read and used today. Because the book was co-authored by the original language designer, and because the first edition of the book served for many years as the de facto standard for the language, the book is regarded by many to be the authoritative reference on C.