Libian (simplified Chinese: 隶变; traditional Chinese: 隸變; pinyin: lìbiàn; lit. 'clerical change') refers to the natural, gradual, and systematic simplification of Chinese characters over time during the 2nd Century BC, as Chinese writing transitioned from seal script character forms to clerical script characters during the early Han dynasty period, through the process of making omissions, additions, or transmutations of the graphical form of a character to make it easier to write. Libian was one of two conversion processes towards the new clerical script character forms, with the other being liding (隸定), which involved the regularisation and linearisation of character shapes.
The earlier seal script characters were complicated and inconvenient to write; as a result, lower-level officials and clerics (隸; lì) gradually simplified the strokes, and transitioned from writing with bowed ink brushes to using straight ink brushes, which both improved ease of writing.
One consequence of the libian transition process is that many radicals formed as a result of simplifying complex components within seal script characters (for example, characters containing "heart" /心 on the side had the component simplified into 忄, as seen in 情 and 恨), and these newly-formed radicals are still used in modern-day Chinese writing as the fundamental basis for constructing and sorting Chinese characters.