Over half a thousand Thai manuscripts are currently being held in British institutions, with the largest collection at the British Library. Other important collections are at the Wellcome Library, the Royal Asiatic Society, the Bodleian Library and the John Rylands Library. Thai manuscripts and historic documents first came to Britain as a result of trade contacts, and documents from the earliest period include official letters and materials received from Thai counterparts. Manuscripts were also brought from Thailand by missionaries, travelers, traders, and officers of the India Office stationed in Burma, others were systematically collected by educators and scholars with a particular research interest. The largest number of manuscripts contains Buddhist scriptures and texts related to Buddhism, many of them in Pali language. However, almost all topics that can be found in the Thai manuscript tradition are represented in the collections held in the UK, for example literary and linguistic works, traditional medicine and healing practices, customary laws, cosmology and astrology, fortune-telling and divination, and animal treatises. Approximately a quarter of these manuscripts are illustrated or decorated in some way; some being outstanding examples of the tradition of Thai manuscript painting and manuscript decoration. This diversity is the result of the different intentions and ambitions of the collectors. Some collectors carefully chose material that they had a certain research interest for. For example, Henry Ginsburg who was fascinated by the beauty of Thai manuscript art built the most important collection of illustrated Thai manuscripts in the UK (held at the British Library). Another collector, Henry Wellcome, was particularly interested in medical texts and artefacts; therefore his collection contains dozens of medical treatises and herbals. Many manuscripts were given to British institutions after the death of a collector, and the trade in manuscripts only began to play a role in the second half of the 20th century. In my article I will give an overview of Thai manuscript collections in the UK, and major contributors and builders of these collections.