This work presents the slotline as an alternative MIC`s transmission line. Special emphasis was given to the slotline design and to the effect of tolerances in various parameters on the performance of the slotline, using sensitivity analysis. The first chapter discusses some previously reported methods of analysis, using a compative approach. The second chapter deals with the desing equations of this kind of transmission line on iso/anisotropic substrate, and the sensibility analysis. Enclosure effects on the electric field configuration are also considered. Chapter 3 presents the characterization of microstrip lines which was necessary to the study of the microstrip- slotine transition. The most usual types of transitions from slotline to coaxial line and to microstrip are studied in the fourth chapter. Especial attention is given to the two-stub microstrip-slotline transition. Optimization methods for broadband desing of single and double transitions are proposed and some practical results are presented. Some of the circuit applications of slotline are discussed in the fifth chapter. The discussion is limited to those slotline circuits which either have some advantages over corresponding microstrip configuration or which are possible anly with slotlines. A powerful synthesis/analysis/optimization software is described in chapter 6. Chapter 7 presents a comprehensive conclusion to the work and points out the author`s original contributions.