Background: Peanut allergy is an immunoglobulin E (IgE)-mediated immune response that usually manifests in childhood and can range from mild skin reactions to anaphylaxis. Since quality of life maybe greatly reduced by the diagnosis of peanut allergy, an accurate diagnosis should always be made. Methods: A selective literature search was performed in PubMed and consensus diagnostic algorithms are presented. Results: Important diagnostic elements include a detailed clinical history, detection of peanut-specific sensitization by skin prick testing and/or in vitro measurement of peanut (extract)-specific IgE and/or molecular components, and double-blind, placebo-controlled food challenge as the gold standard. Using these tools, including published cut-off values, diagnostic algorithms were established for the following constellations: 1) Suspicion of primary peanut allergy with a history of immediate systemic reaction, 2) Suspicion of primary peanut allergy with questionable symptoms, 3) Incidental findings on sensitization testing and peanut ingestion so far or 4) Suspicion of pollen-associated peanut allergy with solely oropharyngeal symptoms. Conclusion: The most important diagnostic measures in determining the diagnosis of peanut allergy are clinical history and detection of sensitizations, also via component-based diagnostics. However, in case of unclear results, the gold standard—an oral food challenge—should always be used.