The term “microfabrication” has been used to denote the technology for manufacturing integrated micro-circuits and microsystems. During the last 30 years the advanced micro-electronics could not maintain its place without microfabrication technology and this is also the case for the present and for the future. Integrated circuits whose fabrication consists of several processes that take place under conditions of higher temperature, vacuum film deposition, oxidation, and dopant implantation are all patterned into circuits by lithography and etching. Microfabrication requires three main ingredients: (i) a lithography tool capable of generating micro-patterns smaller than the minimum required structure dimensions; (ii) a recording medium (resist layer) into which the desired device pattern is written (the mask); and (iii) a pattern transfer-process of the structures created into the resist-relief mask. The aim of this work is to extend Electron-Beam Lithography (EBL) and plasma Reactive Ion Etching (RIE) technology into the manufacturing of Micro Electro Mechanical Systems (MEMS) and sensors. In the first part of this paper the basic aspects of (i) drawing resist-relief mask structures onto the top of the wafers and (ii) pattern transfer of the resist-structures by plasma etching into the substrate will be presented. In later sections, the phenomenas studied will be discussed, which are necessary for the generation of structures with high aspect ratios from the nanometer scale up to the micron scale. Attention will be given to some promising applications and technological procedures for the realization of MEMS and microsensor manufacturing.