The main features of the biennial rhythm in the atmosphere are presented. An interpretation is given of the data on the rhythm in the zonal windspeed in the lower equatorial stratosphere and on the height differences of the 10 mb isobaric surface in two adjacent years (for January in the northern hemisphere) in terms of a cycle with a period of two years and perturbations in the phase of the cycle. The years when perturbations occur are indicated along with the types.