The short answer is many although to qualify that, it partly depends how stress is defined (eg from generalised stress to Acute or post traumatic stress disorder, generalised anxiety . . . ), the 'client group' (eg children, working age adults, older people), the setting (eg outpatient, workplace, school) and whether is is associated with other mental health difficulties (eg depression). For conditions with a formal diagnosis (eg PTSD, Mixed Anxiety Disorders) then Division 12 (Society of Clinical Psychology; APA) has a list of evidence based treatments (https://www.div12.org/psychological-treatments/). Again for formal diagnoses the UK NICE guidelines (https://www.nice.org.uk/guidance) produced to guide commissioners and clinicians about the evidence base for various conditions might also help. In terms of stress reduction (eg in schools, workplace), a number of 'third wave' CBT based self help, online, group and individual based interventions are available (eg mindfulness interventions; compassion based interventions) although the research evidence for these is still emerging.