Protein phosphorylation is the most frequent post-translational modification used to regulate protein activity. Protein kinases, the enzymes that catalyze the phosphoryl transfer, are implicated in practically every aspect of normal as well as abnormal cell functions. Consequently, sensitive, selective, high-throughput and widely applicable methods for monitoring protein kinase activity will provide valuable tools to screen inhibitor candidates for therapeutics and chemical biology, and to unravel the diverse signaling cascades in which these enzymes are pivotal. Peptide-based chemosensors that rely on fluorescence changes upon phosphorylation are highly desirable, because these systems allow a continuous readout offering an excellent spatial and temporal resolution to observe in real time the kinase activity. This tutorial review briefly summarizes the different fluorescent continuous peptide-based strategies that are being commonly employed to sense protein phosphorylation, introduces a few novel and attractive emerging assays, discusses their advantages and limitations, and highlights possible future directions.