Aerosol particle size distribution and concentration are likely the most frequently measured aerosol parameters. In this contribution some methods for determination of aerosol particle size, concentration and refractive index based on the elastic light scattering will be presented. At relatively low concentrations single particle measurement can be applied. An innovative optical system based on a bi- angular scattering from single particles and providing a real-time access to the real and imaginary part of the refractive index of aerosol particles is discussed. The accuracy of the technique has yet to be explored but preliminary findings are presented. Beyond concentration levels of about 103 cm-3 integral observation methods on an ensemble of particles must be used and require usually empirical calibration procedures. A method allowing an absolute, calibration free optical determination of aerosol concentrations up to the order of 108 cm-3 based on a simultaneous measurement of scattered and transmitted light fluxes is presented. Combining elastic scattering measurement with a condensational growth of aerosols gives an access to size distribution of particles based on Kelvin equivalent sizing starting from about 10-3 micrometers in particle radius. The results show that elastic light scattering methods provide a possibility for a real time sizing of aerosols in the size range from about 10-3 micrometers stretching over more than 4 orders of magnitude, for concentration determination starting from single particle counting to about 108 cm-3 and for an assessment of optical properties of aerosols which, if linked with their chemical character, could also have a substantial contribution to industrial and environmental issues.