General Principles

Literally, the concept of life as 'the way'. The 'Tao' or 'way' just is. It's the immutable law of everything. You can fight against it or go with it. Your choice won't make any difference to the Tao, but learning and understanding its nature, may make your own life more fulfilled, rewarding and enlightened.

Historical Background

'Invented' in China in mediaeval times, Taoism (pronounced 'Dow-ism') came about as a reaction to the strict orthodoxy of Confucius and subsequent devotees of Confucianism. Whilst universally acknowledged as containing some very wise truths, Confucianism is very inflexible and could almost be considered dogmatic.
Early Taoists took great delight in debunking some of the myths created by the ruling Confucian orthodoxy - often using ironic humour as their most effective weapon.

Taoism as a Philosophy

Taoism shares much of its philosophical roots with other Eastern religions - particularly Bhuddism, but also draws elements from Hinduism.
Its proponents are on the whole very laid back and relaxed and there is an almost total absence of dogma, but in common with many Eastern philosophies, potential followers of the 'Way' shouldn't expect an easy ride.
Motivation and discipline are very important - as is the seemingly contradictory requirement to approach the experience with open eyes but no expectations.
Yoga, meditation and (non-combative) martial arts are all key components in the Taoist experience.

Taoism as a Religion

Taoism shouldn't really be viewed as a religion - more a design for life and although many fundamentalists would reject the notion, Taoism is actually compatible within just about any belief system.

Further reading

In the UK, the most accessible Taoist 'Guru' is the Barefoot Doctor:

http://www.barefootdoctorglobal.com/

Devotees of A.A. Milne may be interested in:

'The Tao of Pooh' and 'The Te of Piglet' by Benjamin Hoff.