The Serpens cloud has received considerable attention in the last years , in particular the small region known as the Serpens cloud core where a plethora of star formation related phenomena are found .
This review summarizes our current observational knowledge of the cloud , with emphasis on the core .
Recent results are converging to a distance for the cloud of \sim 230 \pm 20 pc , an issue which has been controversial over the years .
We present the gas and dust properties of the cloud core and describe its structure and appearance at different wavelengths .
The core contains a dense , very young , low mass stellar cluster with more than 300 objects in all evolutionary phases , from collapsing gaseous condensations to pre-main sequence stars .
We describe the behaviour and spatial distribution of the different stellar populations ( mm cores , Classes 0 , I and II sources ) .
The spatial concentration and the fraction number of Class 0/Class I/Class II sources is considerably larger in the Serpens core than in any other low mass star formation region , e.g .
Taurus , Ophiuchus or Chamaeleon , as also stated in different works .
Appropriate references for coordinates and fluxes of all Serpens objects are given .
However , we provide for the first time a unified list of all near-IR sources which have up to now been identified as members of the Serpens core cluster ; this list includes some members identified in this review .
A cross-reference table of the near-IR objects with optical , mid-IR , submillimeter , radio continuum and X-ray surces is also provided .
A simple analysis has allowed us to identify a sample of \sim 60 brown dwarf candidates among the 252 near-IR objects ; some of them show near-IR excesses and , therefore , they constitute an attractive sample to study very young substellar objects .
The review also refers to the outflows associated with the young sources .
A section is dedicated to the relatively small amount of works carried out towards Serpens regions outside the core .
In particular , we refer to ISO and to recent Spitzer data .
These results reveal new centers of active star formation in the Serpens cloud and the presence of new young clusters , which deserve follow-up observations and studies to determine their characteristics and nature in detail .
Finally , we give a short , non-exhaustive list of individually interesting Serpens objects .