His short article from 1973 in which he lays out the principles of deep ecology as contrasted with shallow ecology is online here: The Shallow and the Deep, Long-Range Ecology Movement (and probably elsewhere). Some excerpts:
a turning point in our scientific communities. But their message is
twisted and misused. A shallow, but presently rather powerful movement,
and a deep, but less influential movement, compete for our attention. I
shall make an effort to characterize the two.
I. The Shallow Ecology movement:
Fight against pollution and resource depletion.
Central objective: the health and affluence of people in the developed countries.
II. The Deep Ecology movement:
1. Rejection of the man-in-environment image in favor the relational, total-field image. […]
2. Biospherical egalitarianism-in principle. […]
3. Principles of diversity and of symbiosis. […]
4. Anti-class posture. […]
5. Fight against pollution and resource depletion. […]
6. Complexity, not complication. […]
7. Local autonomy and decentralization. […]
See also the Foundation for Deep Ecology, which has a good summary of the movement's history.