This study investigates novel three-dimensional passive microwave components that make use of multilayer technology defined as a production process employing several alternately stacked layers of metal and dielectric structures. Components developed include conventional and equal delay Ruthroff transformers; Guanella baluns; stepped impedance lowpass filters; bandpass filters formed from quarter wavelength stubs and transmission line sections; and balanced transmission lines. The theory of operation of each component is described along with the required design procedures for fabrication in the form of a multilayer MMIC using the Caswell H40 process, or a multilayer MIC using the Hibridas photoimageable thick-film process. New practice includes the development of novel structures including a balanced transmission line with conductors arranged in a broadside configuration; a pseudo coplanar waveguide transmission line with a high characteristic impedance; and a new design of compensated microstrip T-junction with clearly defined reference planes between the three branch lines. An investigation into how certain components operate has resulted in two pieces of new theory which are: a design procedure for bandpass filters formed from quarter wavelength stubs and transmission line sections; and a new theory of operation of equal delay Ruthroff transformers and Guanella baluns which takes into account the parasitic common mode currents. Also included in the thesis are: a brief history of MICs and MMICs including an overview of the different fabrication processes used by industry; a comprehensive description of the Caswell H40 multilayer MMIC process, and the Hibridas photoimageable thick-film process; and a section devoted to test and measurement procedures for circuits fabricated in a MIC or MMIC form using microwave probes, which includes a critical analysis of different calibration and de-embedding methods, and details of suitable test equipment and procedures for testing multiport circuits and circuits with balanced ports.