The Fourth International Conference on Nanochannels, Microchannels and Minichannels ( ICNMM) was held at the University of Limerick in Ireland during June 19 - 21, 2006, under the sponsorship of American Society of Mechanical Engineers. A total of 189 papers were presented and over 250 participants attended the conference. The participants came from 25 countries and presented papers in 22 different areas, including microfluidics, biomedical, heat transfer, single- and two- phase flows, electronics cooling, boiling and condensation, mixing, heat exchangers, and a number of related areas. The participants cited the intense interactions among researchers from various discipline as a major benefit of attending this conference.