Treatment with clear plastic splints became very popular in recent years which can be attributed to a large scale to the introduction of the Invisalign system. The so-called invisible braces are preferred by adult patients who care about their appearance during orthodontic treatment. Even if the request of patients should be taken very serio1usly orthodontist have to know well about the limitations of any treatment modality. This lecture will demonstrate what can be accomplished with the Invisalign system, and how these limits can be expanded. Also, the general advantages and disadvantages of aligner therapy will be described in details.