Abstract: Hazes and clouds are ubiquitous in all substantial atmospheres in the outer solar system. Abundant condensed particles are also inferred from the transmission observations in the warm and hot (500-2200 K) atmospheres of exoplanets which are hundreds to thousands of degrees warmer than the solar system planets. These exotic clouds could result from condensation of salts, silicates and metals, and/or hydrocarbons produced by atmospheric chemistry upon UV radiation. In this presentation, I will first talk about the thin, cold and hazy atmospheres in the outer solar system such as on Saturn’s moon Titan, Neptune’s moon Triton, and Pluto. I will present how these atmospheres regulate themselves such that the chemical-produced hydrocarbon haze particles significantly dominate the radiative energy balance over the gas volatiles. In particular, the haze particles could explain the colder-than-expected temperature on Pluto observed by the New Horizons mission. Then I will talk about the thick, hot and cloudy atmospheres of hot Jupiters and brown dwarfs. I will show how to form clouds of salts, silicates and metals in this regime, highlighting the important physical processes such as seed formation, nucleation, condensation, gravitational settling as well as atmospheric particle transport. I will also emphasize the importance of particle size distribution on interpreting the transmission spectra of exoplanets and how to predict it from first principles in a self-consistent microphysical cloud formation model.