  The mathematical theory of isometric embedding is applied to study the notion
of quasilocal mass in general relativity. In particular, I shall report some
recent progress of quasilocal mass with reference to a cosmological spacetime,
such as the de Sitter or the Anti-de Sitter spacetime, or a blackhole
spacetime, such as the Schwarzschild spacetime. This article is based on joint
work with Po-Ning Chen, Ye-Kai Wang, and Shing-Tung Yau.
