The MESA Research Institute of the University of Twente was created in 1990 through the joining of the research unit Sensors and Actuators with the department of Microelectronics. The multidisciplinary institute, with participation from the faculties of Electrical Engineering, Applied Physics and Chemical Technology, was recently recognized as a Centre of Excellence by the Dutch Science Foundation. It is fully 2 equipped with modem Clean Room facilities (1000 m ) and a number of research laboratories. The objective of MESA is to perform research and development of systems in modem information technology, and on the units on which they are based: the microstructures that process and transduce signals. The institute gradually expanded during the past few years till some 125 persons in 1994. Given the wide variety of research subjects within MESA, it has been decided to start a MESA Monographs series, appearing on a more or less regular, yearly basis. In this way, after some time a good overview of research topics under investigation at MESA will be obtained. The first volume of this series coincides with the Proceedings of pTAS '94, the first Workshop on Micro Total Analysis Systems, held on November 21-22 at the University of Twente in Enschede, The Netherlands. IlTAS has recently been defined as the first strategic research orientation of MESA, aiming at synergetic collaboration between the different disciplines present in MESA.