The Immigration Ordinance is Chapter 115 of Hong Kong's Ordinances. It regulates the immigration issues of Hong Kong such as Right of Abode, immigration control, enforcement of illegal immigration by Immigration Department, etc...
First introduced in 1971 (as Cap 55), it replaced a number of smaller ordinances that dealt with immigration control from China into Hong Kong:
The previous ordinances reflected the flow of immigration prior to establishment of the People's Republic of China in 1949 which resulted in a large movement of immigrants and illegal immigration from the 1950s onwards.
This ordinance is often cited in controversial policies and restrictive nature of immigration in Hong Kong especially in regards to right of abode to non-Chinese immigrants after amendments in 1987 to deal with post-handover Hong Kong.