The experiments performed by researchers in different countries, notably, South Africa, England, Switzerland and the USA, during the last sixty years have greatly advanced our knowledge concerning the mechanism of lightning flashes. However, many pieces of the puzzle are still missing and many of the theories put forth as explanation of its mechanism are mainly of a qualitative nature. The reason for this slow progress is the impossibility of studying lightning flashes under controlled lab oratory conditions. On the other hand, the mechanism of the electric spark, which could be studied under controlled conditions, may guide the researchers in their quest for understanding the mechanism of lightning flashes and creating more advanced theories of the phenomena. After all, it is the observed similarities between the small laboratory sparks and lightning discharges that forced Benjamin Franklin to conclude that the lightning flash is a manifestation of electricity. This chapter is devoted to a description of the mechanism of laboratory sparks.