  During the last few decades, rare isotope beam facilities have provided
unique data for studying the properties of nuclides located far from the
beta-stability line. Such nuclei are often accompanied by exotic structures and
radioactive modes, which represent the forefront of nuclear research. Among
them, two-proton (2p) radioactivity is a rare decay mode found in a few highly
proton-rich isotopes. The 2p decay lifetimes and properties of emitted protons
hold invaluable information regarding the nuclear structures in the presence of
a low-lying proton continuum; as such, they have attracted considerable
research attention. In this review, we present some of the recent experimental
and theoretical progress regarding the 2p decay, including technical
innovations for measuring nucleon--nucleon correlations and developments in the
models that connect their structural aspects with their decay properties. This
impressive progress should play a significant role in elucidating the mechanism
of these exotic decays, probing the corresponding components inside nuclei, and
providing deep insights into the open quantum nature of dripline systems.
