Betazoids are one of the most Humanoid species yet encountered; externally they are indistinguishable from Humans even at close range, differing only in that all Betazoids have a black iris in their eyes.  All Betazoids are natural telepaths thanks to the paracortex, the Betazoid telepathic lobe ; most develop this ability in adolescence, but a few are born with their telepathic abilities already active. Unable to screen out the noise of other peoples minds, these individuals generally suffer mental problems of varying severity.  In general, normal Betazoids develop the ability to protect themselves from psychic trauma through the function of the part of their psyche known as the meta conscious - though severe trauma can overcome this protection. 
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Betazoids can cross-breed with Humans, although this often affects the telepathic abilities of the offspring - sometimes the children of such a union develop empathic rather than telepathic abilities.  All full Betazoids are unable to read the thoughts of Ferengi, Breen, Ullians or Dopterians,  but some half Betazoids have been occasionally successful in sensing the emotions of some of these species. 
Betazoid society is martiarchal in nature, with considerable similarities to the female-dominated world of Angel One.  They tend toward more formal and elaborate traditions and ceremonies than 24th century Earth; for instance titles such as 'daughter of Fifth House, holder of the sacred chalice of Rixx, heir to the holy rings of Betazed' are still carried by some Betazoids. 
At one point in history it became fashionable for Betazoid women to wear large elaborate wigs which contained cages holding small animals. The practice came to an end when one woman took a public stand and refused to go along with the fashion, considering it uncomfortable for the woman and cruel for the animal. 
Arranged marriages are the norm on Betazed, with the arrangement usually agreed between the parents of both parties whilst the couple are still children. Indeed, it is not unknown for couples not to meet until shortly before their wedding. The preparations for the ceremony begin when a 'gift box' is sent to the bride, announcing verbally that the marriage is imminent. Traditional Betazoid weddings are carried out with both the couple and all guests naked. 
The telepathic abilities of Betazoids makes dishonesty rather moot amongst them; many Betazoids pride themselves on being completely honest and speaking their mind forthrightly at all times. 
A Federation member, Betazed has enjoyed a relatively untroubled history for the last few centuries. This peaceful existence came to a halt in 2374, when the Dominion invaded and occupied the planet.  The invasion was ended by the following year when the Dominion forces surrendered at the end of the war with the Allies.