  It has been around fifty years since R. K. Sachs and A. M. Wolfe predicted
the existence of anisotropy in the Cosmic Microwave Background (CMB) and ten
years since the integrated Sachs Wolfe effect (ISW) was first detected
observationally. The ISW effect provides us with a unique probe of the
accelerating expansion of the Universe. The cross-correlation between the
large-scale structure and CMB has been the most promising way to extract the
ISW effect from the data. In this article, we review the physics of the ISW
effect and summarize recent observational results and interpretations.
