Marine eukaryotic phytoplankton are major contributors to global primary production. To adapt and thrive in the oceans, phytoplankton relies on a variety of light-regulated responses and light-acclimation capacities probably driven by sophisticated photoregulatory mechanisms. A plethora of photoreceptor-like sequences from marine microalgae have been identified in omics approaches. Initial studies have revealed that some algal photoreceptors are similar to those known in plants. In addition, new variants with different spectral tuning and algal-specific light sensors have also been found, changing current views and perspectives on how photoreceptor structure and function have diversified in phototrophs experiencing different environmental conditions.