An overview of current traditional tissue and liquid biopsy methods, with a focus on non-small cell lung cancer (NSCLC) is discussed. In order to provide the correct treatment for cancer patients, companion diagnostic tests are required by the FDA for certain medications prior to being prescribed. These tests have to be performed on a patient's tumor sample. Tissue biopsies are the gold standard method for acquiring tumor tissue, however they are highly invasive and inaccurate. Liquid biopsies are becoming more popular, but the technology still poses several limitations.