As a key low-power communication technique, backscatter communications exploits the reflected or backscattered signals to transmit data, where the backscattered signals can be the reflection of ambient radio frequency (RF) signals, the RF signals from the dedicated carrier emitter or the signal photons in the non-classical quantum entangled pairs, etc. In the past 70 years, various kinds of backscatter communication systems have been developed, which will enable the low-power communications as required in the Internet of things (IoTs) and green communications. This article provides a historical view on the development and the research achievements on backscatter communications, including the fundamental principles, the applications, the challenges, and the potential research topics. This article will benefit the researchers and engineers concerning the area of backscatter communications, especially for applications in IoTs.