At some point in their history the formed the Andorian Empire. By the 20th century they had made contact with the Vulcans. Relations with the Vulcans staled and border dispute between the two species began in the mid-20th century and would last for a further 200 years. (ENT: "Proving Grounds")
Relations between the Andorians and Vulcans improved thanks to the efforts of United Earth, up to the point where in 2161 the Andorians became one of the first members of the new United Federation of Planets, which also included the Vulcans. (ENT: "Zero Hour"; TNG: "Outcast")
In appearance Andorians were usually blue-skinned with white or silver hair. The colour of their blood was also blue. They had a pair of antenna on their heads, which could be used to signify their emotions as well as helping with their balance. If lost they would grow back in around nine months. (ENT: "United"; DS9: "The Sound of Her Voice")
The chan gender and thaan gender roughly correspond to male while the shen and zhen genders roughly correspond to female.
During reproductive process the thaan would fertilise the shen. The chan then adds his gametes to the shen. The shen then transfers the zygote to the zhen's pouch who carries it to term. The zhen does not contribute genetically to the child. (DS9 relaunch novels)
Andorians use a name prefix before their family name to indicate their gender.
- Chan – ch' (eg. Veeyel'tar ch'Quait)
- Shen – sh'
- Thaan – th' (eg. Azihagiser th'Hist)
- Zhen – zh' (eg. Lasalat zh'Neek)