Phenomenology is a philosophical tradition or movement of the first half of the 20th Century, developed largely by the German philosophers Edmund Husserl and Martin Heidegger, which is based on the premise that reality consists of objects and events ("phenomena") as they are perceived or understood in the human consciousness, and not of anything independent of human consciousness.
It is the study of experience and how we experience. It studies structures of conscious experience as experienced from a subjective or first-person point of view, along with its "intentionality" (the way an experience is directed toward a certain object in the world). It then leads to analyses of conditions of the possibility of intentionality, conditions involving motor skills and habits, background social practices and, often, language. For more details, see the section on the doctrine of Phenomenology.
As a branch of Philosophy of Mind, it has been central to the European Continental Philosophy tradition for most of the 20th Century. Many of it proponents, however, claim that it is related to, but quite distinct from, the other key disciplines in philosophy (Metaphysics, Epistemology, Logic and Ethics), and that it represents more a distinct way of looking at philosophy which has repercussions on all of these other fields.
Phenomenology, as it is understood today, is essentially the vision of one man, Edmund Husserl, which he launched in his "Logical Investigations" of 1901, although credit should also be given to the pioneering work on intentionality (the notion that consciousness is always intentional or directed) by Husserl's teacher, the German philosopher and psychologist Franz Brentano (1838 - 1917) and his colleague, Carl Stumpf (1848 - 1936).
Husserl formulated his classical Phenomenology first as a kind of "descriptive psychology" (sometimes referred to as Realist Phenomenology) and later as a transcendental and eidetic science of consciousness (Transcendental Phenomenology). In his "Ideas" of 1913, he established the key distinction between the act of consciousness ("noesis") and the phenomena at which it is directed (the "noemata"). In his later transcendental period, Husserl concentrated more on the ideal, essential structures of consciousness, and introduced the method of phenomenological reduction specifically to eliminate any hypothesis on the existence of external objects.
Martin Heidegger criticized and expanded Husserl's phenomenological enquiry (particularly in his "Being and Time" of 1927) to encompass our understanding and experience of Being itself, and developed his original theory of "Dasein" (the non-dualistic human being, engaged in the world). Husserl charged Heidegger with raising the question of ontology but failing to answer it, but Heidegger's development of Existential Phenomenology greatly influenced the subsequent flowering of Existentialism in France.
The movement split between the three main types of Phenomenology (Realist Phenomenology, Transcendental Phenomenology and Existential Phenomenology), each sub-branch having its own adherents. Husserl's early Realist Phenomenology was prefered by the Munich Group at the University of Munich in the early 20th Century, led by Johanes Daubert (1877 - 1947) and Adolf Reinach (1883 -1917), as well as Alexander Pfänder (1871 - 1941), Max Scheler (1874 - 1928), Roman Ingarden (1893 - 1970), Nicolai Hartmann (1882 - 1950) and Hans Köchler (1948 - ). Transcendental Phenomenologists include (in additon to Husserl himself) Oskar Becker (1889 - 1964), Aron Gurwitsch (1901 - 1973) and Alfred Schutz (1899 - 1959). Followers of Heidegger's Existential Phenomenology include Jean-Paul Sartre, Hannah Arendt (1906 - 1975), Emmanuel Levinas (1906 - 1995), Gabriel Marcel (1889 - 1973), Paul Ricoeur (1913 - 2005) and Maurice Merleau-Ponty (1908 - 1961).