"Always design your programs as a member of a whole family of programs, including those that are likely to succeed it"

"Separate Concerns"

"A Programming Language is a tool that has profound influence on our thinking habits"

"The competent programmer is fully aware of the strictly limited size of his own skull; therefore he approaches the programming task in full humility, and among other things he avoids clever tricks like the plague" (from 1972 Turing Award Lecture)

"Progress is possible only if we train ourselves to think about programs without thinking of them as pieces of executable code"

"Program testing can best show the presence of errors but never their absence"

"I mean, if 10 years from now, when you are doing something quick and dirty, you suddenly visualize that I am looking over your shoulders and say to yourself, "Dijkstra would not have liked this", well that would be enough immortality for me"