Teleology (Greek telos, “end”; logos, “discourse”), in philosophy, the science or doctrine that attempts to explain the universe in terms of ends or final causes. Teleology is based on the proposition that the universe has design and purpose.

There is not one but a number of forms of Teleology.  Some of these can be listed here.

In Aristotelian Philosophy, the explanation of, or justification for, a phenomenon or process is to be found not only in the immediate purpose or cause, but also in the “final cause”—the reason for which the phenomenon exists or was created.  Every object has a material cause (the substance it is made from), an efficient cause, a final cause etc.  Platonic and Neoplatonic theories of creation would also fall under this heading.

Monotheistic Creationism, which holds the existence of an external deity who has designed the world, represents Dualistic Teleology.  In Christian theology, teleology represents a basic argument for the existence of God, in that the order and efficiency of the natural world seem not to be accidental. If the world design is intelligent, an ultimate Designer must exist. This is the so-called argument by design that was used by theologians right up until Darwin's day.  The teleological argument for the existence of God holds that order in the world could not be accidental and that since there is design there must be a designer.  e.g. if you see a watch lying in the sand you assume someone built it (in a factory, say) because it is inconceivable that such a complex structure could arise by chance.  Similarily it is argued that complex things like living beings could not have possibly arisen through chance.

Teleologists, like Vitalists, oppose mechanistic interpretations of the universe that rely solely on organic development or natural causation. Darwin's theories of evolution, which hold that species develop by natural selection, was devestating to teleolgy, because it showed that complex structures like living organisms could arise through "chance".  Teleological arguments for Design were revived however during the upsurge of creationist sentiment in the early 1980s onwards.

Science in general is very histile to teleology, because of its metaphysical and theological implications.  However, one scientifically valid evolutionary view finds purpose in the higher levels of organic life but holds that it is not necessarily based in any transcendent being.  There are in fact two different teleologies here.  As Dr. Francisco Ayala explains:

"We may distinguish two kinds of natural teleology: bounded, or determinate or necessary, and unbounded or indeterminate or contingent.

Bounded natural teleology exists when specific end-state is reached in spite of environmental fluctuations. The development of an egg into a chicken is an example of bounded natural teleological process. The regulation of body temperature in a mammal is another example. In general, the homeostatic processes of organisms are instances of bounded natural teleology.

Unbounded design or contingent teleology occurs when the end-state is not specifically predetermined, but rather is the result of selection of one from among several available alternatives. The adaptations of organisms are designed, or teleological, in this indeterminate sense. The wings of birds call for teleological explanation: the genetic constitutions responsible for their configuration came about because wings serve to fly and flying contributes to the reproductive success of birds. But there was nothing in the constitution of the remote ancestors of birds that would necessitate the appearance of wings in their descendants. Wings came about as the consequence of a long sequence of events, where at each stage the most advantageous alternative was selected among those that happened to be available; but what alternatives were available at any one time depended, at least in part, on chance events."

Dr. Francisco Ayala -Teleology and Teleological Explanations

An alternative and perhaps the most sophisticated form of Teleology is Process Teleology.  This holds that creation or evolution is guided, not from an external deity, but from an inherent unfolding within the creature or object that is evolving.  In a sense it combines the previous explanations in a single holistic, pantheistic, or panentheistic, explantion of the universe.

According to this position evolution is goal directed, and the cosmos is not aimless, but a dynamic movement towards greater self-unfoldment.  The universe can even be understood as unfolding along a sequence of pre-defined stages, and entities evolve through specific archetypal modes or kingdoms, in which the ultimate stage can be referred to as "God".  Divinity is therefore not an external creator, but a state to be achieved.

Several very interesting forms of alternative Process and Unified Science - e.g. the hypotheses of  Arthur M. Young and  Edward Haskell, are based on this kind of process Teleology.  Similarily the evoluutionary philosophies of Theosophy, Teilhard de Chardin,  and Sri Aurobindo.

some material on this pagetaken from "Teleology," Microsoft (R) Encarta. Copyright (c) 1994 Microsoft Corporation. Copyright (c) 1994 Funk & Wagnall's Corporation.

Links - Teleology

Teleology- short intro

Teleology - listing in the Catholic Enclyclopaedia - philosophical and theological coverage, I find this sort of stuff dry and technical

Teleology and Teleological Explanations - argues for "natural" as opposed to supernatural (theological)  teleology

CRITICAL-CAFE: Darwinism and teleology - and Darwinism and epistemology - oon-going discussion - philosophical

Teleology - this is the same as the Encarta text