Based on testing results, the authors conclude that if standards are available, optical microscopy is by far the best method for distinguishing among polyethylene films. The structural and chemical differences between the films were marginal, but the different manufacturing processes clearly produced measurable differences in the textures of the films, which can be identified with optical microscopy. Phase contrast microscopy may be slightly better than differential interference contrast microscopy. The testing determined that X-ray diffraction was the most effective method for classifying the type and category to which a particular polyethylene belonged, i.e., low-density, linear low-density, or high-density. In individualizing the films, reasonable discrimination was achieved by using ZnSe ATR infrared spectroscopy. Using classification software, samples can easily be classified individually. Plastic bags are often selected as evidence from crime scenes, and it may be important to distinguish their characteristics in linking them to different criminal events. The 31 bags selected for analysis in the current study were colorless, transparent plastic bags commonly found in homes. These types of bags are often used to package drugs. This paper describes the procedures used in each of the testing methods. 1 table, 19 figures, and 3 references