The rapid development of solid-state lighting technologies has been the stimulus for visible light communications (VLC) to be the focus of enormous interest over the last decade. The key feature of simultaneous data transmission and illumination using white light-emitting diodes (LEDs) makes VLC a potential candidate for future power efficient communication networks that aim to meet the ever-increasing demands for high-speed internet services. Researchers, motivated by the success of VLC technology, have developed a number of techniques and methods to support communication systems with both high transmission speeds and spectral efficiency. Here, we provide an overview of the multi-band carrier-less amplitude and phase (m-CAP) modulation technique enabling highly spectrally efficient VLC links in bandlimited environments. Index Terms-multi-band carrier-less amplitude and phase modulation, spectral efficiency, visible light communications I. INTRODUCTION HE existing radio frequency (RF) based wireless communication technologies cannot cope with the increasing demands for high-speed data traffic, which is expected to grow sevenfold between 2016 and 2017 [1]. The commercially available RF spectrum has already been exhausted, thus leading to the spectrum crunch that needs urgent attention. There are a number of possible options to address this problem including allocation of new spectra, which is highly expensive, spectrum hoping, sharing and borrowing, advanced modulation and coding schemes, interference elimination, and parallel transmission. Alternatively, the carrier frequency could be shifted to the optical domain i.e., optical wireless communications (OWC), which covers the three main bands of visible, infrared and ultraviolet, thus offering an alternative solution for future broadband services in indoor and outdoor environments [2]. The infrared and ultraviolet bands are mostly used in outdoor applications for line-of-sight (LOS) and non-LOS links, whereas the visible band has been widely adopted in the indoor environment [3]. As a part of OWC, visible light communications (VLC) has been the focus of enormous attention due to a few key advantages including (i) high and unregulated bandwidth (in the order of THz);