Brown Dwarfs are the coolest class of stellar objects known to date .
Our present perception is that Brown Dwarfs follow the principles of star formation , and that Brown Dwarfs share many characteristics with planets .
Being the darkest and lowest mass stars known makes Brown Dwarfs also the coolest stars known .
This has profound implication for their spectral fingerprints .
Brown Dwarfs cover a range of effective temperatures which cause brown dwarfs atmospheres to be a sequence that gradually changes from a M-dwarf-like spectrum into a planet-like spectrum .
This further implies that below an effective temperature of \lesssim 2800 K , clouds form already in atmospheres of objects marking the boundary between M-Dwarfs and brown dwarfs .
Recent developments have sparked the interest in plasma processes in such very cool atmospheres : sporadic and quiescent radio emission has been observed in combination with decaying Xray-activity indicators across the fully convective boundary .