In the second half of the 20th century, the Irish dairy industry - in common with the experience of agriculture throughout developed market economies - has been subject to restructuring processes arising from what some writers have termed the second agricultural revolution (Healy and Ilbery 1985) but which Bowler (1992) more correctly refers to as the third such revolution. This involves "the progressive extension of technological, organisational and economic rationality into the arena of farm operations, linking them even more closely to the other sectors of the economy, both materially and in ethos" (Wallace 1984, quoted in Healy and Ilbery 1985: 2). The specific outcomes of this rationalisation process have been summarised by Bowler (1992) under the three headings: intensification, concentration and specialisation. This paper traces the process of rationalisation in the Irish dairy industry in the 20th century and discusses some of its economic and social outcomes, with particular reference to its impact on communities of small dairy farmers. Initially however, the paper provides some background information on Irish agriculture in general, and on the early growth of the Irish dairy cooperative sector in the late 19th and early 20th centuries.