Molecular imaging plays important roles in many fields, including disease diagnosis, therapeutic efficacy evaluation, intraoperative imaging guidance, drug metabolism monitoring, and patient selection for appropriate treatment. As a key component, the targeting ligand determines the specificity, affinity, and in vivo performance of molecular imaging probes. In this review, high-throughput screening and biological display platforms for the discovery of ligands applicable to molecular imaging are briefly reviewed. Basic information on ligand development for molecular imaging is first introduced, followed by a presentation of various selection platforms and typical or iterative cases. The features, advantages, limitations, and application scope of screening and display platforms are compared and discussed. Last, a basic selection strategy and a perspective for protein-based ligands are provided.