Neuroendocrine tumors (NET) constitute a heterogeneous group of malignancies with various clinical presentations and growth rates but a common origin in neuroendocrine cells located all over the body. NET are a relatively low-frequency disease mostly represented by gastroenteropancreatic (GEP) and bronchopulmonary tumors (pNET); on the other hand, an increasing frequency and prevalence have been associated with NET. Despite great efforts in recent years, the management of NET is still a critical unmet need due to the lack of knowledge of the biology of the disease, the lack of adequate biomarkers, late presentation, the relative insensitivity of imaging modalities, and a paucity of predictably effective treatment options. In this context Ca²⁺ signals, being pivotal molecular devices in sensing and integrating signals from the microenvironment, are emerging to be particularly relevant in cancer, where they mediate interactions between tumor cells and the tumor microenvironment to drive different aspects of neoplastic progression (e.g., cell proliferation and survival, cell invasiveness, and proangiogenetic programs). Indeed, ion channels represent good potential pharmacological targets due to their location on the plasma membrane, where they can be easily accessed by drugs. The present review aims to provide a critical and up-to-date overview of NET development integrating Ca²⁺ signal involvement. In this perspective, we first give an introduction to NET and Ca²⁺ channels and then describe the different families of Ca²⁺ channels implicated in NET, i.e., ionotropic receptors, voltage-dependent Ca²⁺ channels, and transient receptor potential channels, as well as intracellular Ca²⁺ channels and their signaling molecules.