威塞克斯（英语：Wessex）意即西撒克逊（West Saxons），是盎格鲁-撒克逊人的一个王国。其立国时间是519年左右，开国者据说是率族人登陆英格兰汉普郡沿海地带的彻迪克。

到了彻迪克的孙子查乌林（在位期间560年－593年）时，撒克逊人的定居点已经遍布希尔腾山脉，原先的居民凯尔特人则被撒克逊人从泰晤士河上游河谷和塞文河下游之间的区域驱逐出去，但查乌林本人却被撒克逊人放逐。

直到8世纪末，威塞克斯王国一直处于强国的阴影下——先是肯特，然后是诺森布里亚，最后是麦西亚。不过这一时期威塞克斯也并非毫无作为，国王卡德瓦拉（在位期间685年－688年）对邻国开展了几次成功的战役，他的继承者因尼一方面向西面的布立吞人小王国扩展领土，一方面迫使肯特进贡。因尼死后，威塞克斯陷入了混乱状态中。

Wessex (/ˈwɛsᵻks/; Old English:Westseaxna rīce, "kingdom of the West Saxons") was an Anglo-Saxon kingdom in the south of Great Britain, from 519 until England was unified by Æthelstan in the early 10th century.

The Anglo-Saxons believed that Wessex was founded by Cerdic and Cynric, but this may be a legend. The two main sources for the history of Wessex are the Anglo-Saxon Chronicle and the West Saxon Genealogical Regnal List, which sometimes conflict. Wessex became a Christian kingdom after Cenwalh was baptised and was expanded under his rule. Cædwalla later conquered Sussex, Kent and the Isle of Wight. His successor, Ine, issued one of the oldest surviving English law codes and established a second West Saxon bishopric. The throne subsequently passed to a series of kings with unknown genealogies.