The definition of complete resection in neurosurgery depends on tumor type, surgical aims, and postoperative investigations, directly guiding the choice of intraoperative tools. Most common tumor types present challenges in achieving complete resection due to their infiltrative nature and anatomical constraints. The development of adjuvant treatments has altered the balance between oncological aims and surgical risks. We review local recurrence associated with incomplete resection based on different definitions and emphasize the importance of achieving maximal safe resection in all tumor types. Intraoperative techniques that aid surgeons in identifying tumor boundaries are used in practice and in preclinical or clinical research settings. They encompass both conservative and invasive techniques. Among them, morphological tools include imaging modalities such as intraoperative magnetic resonance imaging, ultrasound, and optical coherence tomography. Fluorescence-guided surgery, mainly using 5-aminolevulinic acid, enhances gross total resection in glioblastomas. Nuclear methods, including positron emission tomography probes, provide tumor detection based on beta or gamma emission after a radiotracer injection. Mass spectrometry– and spectroscopy-based methods offer molecular insights. The adoption of these techniques depends on their relevance, effectiveness, and feasibility. With the emergence of positron emission tomography imaging for use in recurrence benchmarking, positron emission tomography probes raise particular interest among those tools. While all such tools provide valuable insights, their clinical benefits need further evaluation.