The survey techniques ofr finding quasars in large areas of sky have developed rapidly in recent years. One can search for quasars in all wavelengths. The area of sky surveyed may be more than 1000 square degrees. The average density of quasar candidates down to magnitude 20is about 20 per square degree. Therefore, more than 20000 quasar candidates are waiting for further observation. the total number of confirmed quasars is currently about 5000. This paper gives a discussion of some of the physical properties of quasars, such as space distribution, luminosity function, clustering and redshift limit.