This is a longitudinal study where individual with Major Depressive Disorder (MDD) will be monitored for 12 weeks. The study aims to develop an objective, sensor-based, algorithm able to detect the presence of depression as well as predict treatment response. Measurement-based treatment is considered optimal and the development of a valid passive, objective, behavioral and biological assessment of depressive symptoms that does not rely on clinician interviews will improve monitoring and ultimately improve treatment significantly.

In this longitudinal study 100 individuals with Major Depressive Disorder (MDD) will be monitored for 12 weeks. Data will include self-report surveys, in-person assessments, physiological features derived by wearable devices and socialization and activity data derived by mobile applications. The study will utilize advanced statistical methods to integrate different sources of passive sensor-based behavioral and physiological data to develop models able to detect depression and predict treatment response.

Inclusion Criteria:

1. Adults (ages 18-75),
2. Able to read, understand, and provide written informed consent in English,
3. Meet criteria for a primary psychiatric diagnosis of current major depressive disorder
4. Hamilton Depression Rating Scale (HDRS) total score ≥ 18,
5. Must have measurable skin conductance/electrodermal activity (as assessed at the screening visit),
6. Must own a working smartphone and use it regularly,
7. Must own a windows PC (or tablet) or a Mac computer (or laptop),
8. Must have access to Internet service every day.
9. Must have started antidepressant medications, changed medication dosage, or started therapy within 3 weeks

Exclusion Criteria:

1. Active drug or alcohol use disorder in the past 3 months,
2. History of psychotic disorder,
3. History of mania or hypomania,
4. Epilepsy or history of Seizure Disorder (including PNES), narcolepsy, Alzheimer Disease, Parkinson's Disease, ALS, Severe TBI, Dementia, MS, Cerebral Palsy, and Neuralgia.
5. Untreated hypothyroidism,
6. Unstable medical disease,
7. Cognitive impairment that would impede adherence to study procedures,
8. Acute suicide or homicide risk,
9. Current treatment with electroconvulsive therapy, vagal nerve stimulation therapy, deep brain stimulation, transcranial magnetic stimulation therapy, or phototherapy,
10. Cannot comprehend or communicate in English,
11. Lack of working smartphone or lack of daily access to Internet service,
12. Inability to measure skin conductance/electrodermal activity (as assessed at the screening visit), and
13. Inability or unwilling to, at minimum, wear the physiological sensor (E4) wristbands, download monitoring apps, and fill out the surveys.
14. Participants with more than two treatment failures (more than two adequate trials of meds on the basis of ATRQ) in the current mood episode.

Participants will be individuals with Major Depressive Disorder