In the United States, most probiotic products are either foods or dietary supplements. A few probiotics are marketed as medical foods. Although fermented dairy products such as yogurt and kefir are typically associated with delivery of "beneficial cultures", the types of foods claiming to deliver probiotics has expanded to include granola and candy bars, frozen yogurt, cereal, juice and cookies. Whether or not any given product, even ones that claim to contain "probiotics", actually deliver adequate amounts of efficacious probiotic strains cannot be ascertained from just looking at the product. In general, consumers need to contact the manufacturer to determine what studies have been conducted on their specific product as formulated and what health benefits should be expected.

In food products, the probiotics used are primarily species of Lactobacillus or Bifidobacterium, or Streptococcus thermophilus.

In the United States, yogurt is required to be produced by the fermentation by Lactobacillus bulgaricus and Streptococcus thermophilus. However, post-fermentation heat treatment of yogurt, which kills all live cultures, is allowed. To help consumers distinguish between yogurts that contain live active cultures and those that do not, the National Yogurt Association established a "Live Active Culture" seal. The seal is available for use by any yogurt manufacturer on packaging and requires refrigerated yogurt to contain 10⁸ viable lactic acid bacteria per gram at the time of manufacture. The seal also can be used on frozen yogurts containing 10⁷ viable lactic acid bacteria per gram at time of manufacture. However, these counts do not differentiate probiotic bacteria from starter culture bacteria (L. bulgaricus and S. thermophilus), and therefore the seal is not useful in determining if adequate levels of added probiotic bacteria are present in a yogurt. In other words, the standard refers to a total number of live cultures and levels of each microbe present do not have to individually meet the standard. The NYA is also currently petitioning the United States government to have the standard of identity of yogurt changed to require that the starter cultures be viable in the finished yogurt.

The dietary supplement market for probiotic cultures seems to be a more diverse and more active market than probiotics for dairy. The supplement market contains many different product formats and contents, including capsules, liquids, tablets and even food-like formats. If properly prepared and stored, probiotic bacteria can remain viable in dried form and reach the intestine alive when consumed. A diverse array of bacterial genera and species are represented in these products, including many different lactobacilli, bifidobacteria and less commonly, Enterococcus, Bacillus, Escherichia coli and yeast. Dietary supplement products are purchased primarily in health food stores or natural foods grocery stores.