During the period from 1979 to 1999 the rate of the decrease in the global annual mean value of total ozone content (TOC) is found to be about 2.5% per decade. In midlatitudes and high latitudes of the northern hemisphere this decrease is mainly due to more frequent occurrence and higher magnitudes of negative anomalies in TOC observed in the period from 1987 to 1997. In the past two years in mid and high latitudes of the northern hemisphere the increase of TOC up to the magnitudes typical for the middle 70s was observed. Satellite observations show that the Antarctic ozone "hole" during the spring period, which was clearly revealed in the annual variation of TOC at southern latitudes higher than 60°S in 1960-1970, either continues to grow or reached its maximum in 1998. The TOC increase observed in the past two years cannot be caused by the efforts taken to overcome the anthropogenic effect on ozone layer since the TOC increase is observed under conditions of maximal concentration of stratospheric chlorofluorocarbons. Nowadays, scientific concepts on the state and causes of the observed evolution of the ozone layer are not clearly understood, and, in particular, prevent prediction of the observed sharp changes in ozone layer and the occurrence of isolated anomalies in the northern hemisphere.