David Lockwood's distinction between "social integration" and "system integration" has had a huge impact on Jürgen Habermas's social theory. It was introduced by Lockwood in 1964 in an article in "Explorations in Social Change" (ed. by George K. Zollschan and Walter Hirsch; Routledge). The article is also available in David Lockwood's excellent book "Solidarity and Schism: The Problem of Disorder in Durkheimian and Marxist Sociology" (Clarendon Press, 1992).
See the obituary in the Guardian here.