DBT is a branch of CBT that attempts to address the deficits of CBT. DBT places emphasis on the psychosocial components of CBT by focusing on how therapists can help clients have productive interactions with others. DBT focuses on assisting clients to manage their emotions and reduce conflicts in interpersonal relationships.
In contrast, CBT focuses on helping patients reframe their thoughts in a way that addresses their psychological problems. CBT helps clients use logic and reasoning to manage negative thought patterns and take control of their lives.
Another difference is that CBT is used to treat a wide range of mental illnesses while DBT focuses on illnesses that are associated with negative emotions, such as borderline personality disorder. CBT is effective on depression and OCD while DBT is effective on self-harm and chronically negative emotions.
CBT focuses on reasoning out problems using critical thinking and rationalization while DBT focuses on calming down techniques that help the patient cope with problems and accept them instead of fighting them.
Most CBT sessions apply individualized treatment while DBT is most suited to group therapy.