This paper reviews the recent development of the Boolean Single Flux Quantum (BSFQ) circuits. BSFQ circuits perform Boolean operation based on the superconducting flux level, and let digital bits propagate in the form of 'set' and 'reset' pulses using dual-rail Josephson transmission line (JTL). Just the same as CMOS circuits BSFQ circuits do not require any local clock system for the operation gates, and thus are delay insensitive, and comparably simple in terms of the number of Josephson junctions. Implementation of basic BSFQ circuits, namely 'NOT,' 'AND,' 'OR,' 'XOR' gate, is described. These circuits have been experimentally tested, and their workability has been proven.