Abstract: An improved printed circuit board arrangement is disclosed which is especially suited for use in miniaturized electrical or electronic apparatus. A first printed circuit board is provided for accommodating a plurality of circuit components and designed to accomplish predetermined operational capabilities. Additional operating features may be readily and conveniently provided by separate option circuit boards which may be selectively interconnected to the first or main chassis board. The interconnection is effected by a pair of guide rails which engage respective edge portions along the sides of the two circuit boards and maintain the same in an edge-to-edge, coplanar relation. The boards may be permanently secured together by any suitable soldering process. Electrical interconnection is accomplished by a ribbon flex harness with printed conductors and connection terminals at respective ends which engage suitable connection terminals on the associated circuit boards.