Special issue on fundamental principles and techniques in microfluidics.

About a year ago we were charged, by the Lab on a Chip Editorial Board, to edit a themed issue on fundamental principles and techniques in microfluidics. The outcome is this set of nontraditional reviews, each written as a primer for those in the Lab on a Chip audience unfamiliar with the specific topic and/or as a critical review of recent developments for more advanced researchers. Since microfluidics has expanded rapidly in the past two decades to a field with a variety of dedicated journals, we have made no attempt to be exhaustive in covering all topic areas. Instead, we chose to cover a few topics which are fundamental to implementing microfluidic functionalities required for lab on a chip devices and systems.