I've come to find the following really useful. This is how you can map the Tab key in insert mode while still being able to use it when at the start of a line or when the preceding char is not a keyword character. in a script file in a plugin directory or in your .vimrc file: first define a function which returns a Tab or the appropriate completion, depending on the context: Then define the appropriate mappings: inoremap =Smart_TabComplete() The trick here is the use of the = in insert mode to be able to call your function without leaving insert mode. See [help i_CTRL-R].