A personal union is the combination by which two or more different states have the same monarch while their boundaries, their laws and their interests remain distinct. It should not be confused with a federation which is internationally considered a single state. Nor is it to be confused with dynastic union, where the union can be under a dynasty.

Personal unions can arise for very different reasons, ranging from coincidence (a princess who is already married to a king becomes queen regnant, and their child inherits the crown of both countries) to virtual annexation (where a personal union sometimes was seen as a means of preventing uprisings). They can also be codified (i.e., the constitutions of the states clearly express that they shall share the same person as head of state) or non-codified, in which case they can easily be broken (e.g., by the death of the monarch when the two states have different succession laws).

Because presidents of republics are ordinarily chosen from within the citizens of the state in question, personal unions are almost entirely a phenomenon of monarchies, the unique exception in modern times being the Principality of Andorra in which one of the two co-princes is the President of France, while the other is a Roman Catholic bishop. Sometimes the term dual monarchy is used to signify a personal union between two monarchies.

James Hudson Taylor (Chinese: 戴德生) (21 May 1832 – 3 June 1905), was a British Protestant Christian missionary to China, and founder of the China Inland Mission (CIM) (now OMF International). Taylor spent 51 years in China. The society that he began was responsible for bringing over 800 missionaries to the country who began 125 schools and directly resulted in 18,000 Christian conversions, as well as the establishment of more than 300 stations of work with more than 500 local helpers in all eighteen provinces.

Taylor was known for his sensitivity to Chinese culture and zeal for evangelism. He adopted wearing native Chinese clothing even though this was rare among missionaries of that time. Under his leadership, the CIM was singularly non-denominational in practice and accepted members from all Protestant groups, including individuals from the working class and single women as well as multinational recruits. Primarily because of the CIM's campaign against the Opium trade, Taylor has been referred to as one of the most significant Europeans to visit China in the 19th Century. Historian Ruth Tucker summarises the theme of his life: