Russel's most important contribution in mathematical logic occured in the early 1900's when he collaborated with Alfred Whitehead on the three-volume "Principia Mathematica". They attempted to demonstrate that all pure mathematics follows from premises that are strictly logical and uses only those concepts that can be defined in purely logical terms.

His most popular book is probably "A History of Western Philosophy" published in 1945. Russell expressed his social and political ideas in numerous works and essays written over a seventy year period of time. He also wrote many accounts of his life, including an autobiography published from 1967-69.

Bertrand Russell was an outspoken pacifist and advocated very liberal attidudes towards sex, marriage and methods of education. He was a critic of World War I and was imprisoned in 1918 for anti-war propaganda, and again in 1961 for "incitement to civil disobedience" in a campaign for nuclear disarmament.

A week before Albert Einstein died, Bertrand Russell asked the physicist to sign a appeal to stop all nuclear testing, an act that bore fruit in the nucelar test ban treaty in 1963. This letter became famous as the Einstein/Russell appeal.

Quotes :
'The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts.'

'Government can easily exist without law, but law cannot exist without government.'