Peroral drug application is the most preferred by patients and clinicians, but is also connected with many problems such as pH or enzymatic drug degradation in gastrointestinal tract or metabolic inactivation after first pass in liver. By applying the drug on oral cavity mucosa, this problems may be avoided. Oral cavity mucosa is relatively permeable, has a rich blood supply is robust and shows short recovery time after stress or damage. Drug absorbed via oral cavity mucosa bypasses first pass metabolism in gastrointestinal tract and liver and avoids gastrointestinal side effects. Sublingual mucosa is relatively permeable, gives rapid absorption and acceptable bioavailabilities for many drugs. Sublingual drug application is today widely used in treatment of angina pectoris. Buccal mucosa is more robust and less permeable than sublingual area and is not able to provide rapid absorption and is more suitable for sustained and controled release devices. Different absorption enhancers could increase drug bioavailability. Mucoadhesive polymers ensure tight contact between drug delivery devices and buccal mucosa and thereby they increase bioavailability of applied drug and provide dosage form retention. The most used mucoadhesive polymers are acrylic acid polymers, different cellulose esters, some natural polymers (chitosan) and gums (guar, pectin, alginate). Bioadhesive dosage forms in the buccal cavity include adhesive tablets, adhesive gels and patches. According to some recent results we could expect increase ofnumber of commercially available systems in near future.