General Mental Health
Mental Health by Harvard Medical School

Individual Therapy
FAQs about Psychotherapy by Jim Haggerty, M.D.

Group Therapy
5 Benefits of Group Therapy by Margarita Tartakovsky, M.S. 

Cognitive Psychotherapy
About Cognitive Psychotherapy by Michael Herkov, Ph.D. 
In-Depth: Cognitive Behavioral Therapy by Ben Martin, Psy.D.

Addiction
National Institute on Drug Abuse
National Institute on Alcohol Abuse and Alcoholism
Substance Abuse and Mental Health Services Administration
Addiction by Harvard Medical School 
How Addiction Hijacks the Brain by Harvard Medical School
What Does It Mean When We Call Addiction A Brain Disorder? By Scientific American

ADHD
Adult and Child ADHD by Harvard Medical School
Attention Deficit Hyperactivity Disorder by the National Institute of Mental Health

Anxiety
Anxiety by Harvard Medical School
Anxiety Disorders by the National Institute of Mental Health
Psychotherapy Guide for Generalized Anxiety Disorder by Verywell Mind

Bipolar Disorder
Bipolar Disorder by the National Institute of Mental Health
What Should You Know About Bipolar Disorder?  By Christian Nordqvist, Medical News Today
Bipolar disorder articles from Psych Central

Depression 
Depression by Harvard Medical School
Depression by the National Institute of Mental Health
Depression by John M. Grohl, Psy.D. 
Men and Depression by the National Institute of Mental Health

Schizophrenia
Schizophrenia by the National Institute of Mental Health
Biological Origin of Schizophrenia by Harvard Medical School
Scientists Move Closer to Understanding Schizophrenia's Cause by Benedict Carey, The New York Times

Stress
The Danger of Stress by Melinda Wenner, Scientific American
7 Startups that Want to Improve Your Mental Health  by CNN

Gambling
How the Brain Gets Addicted to Gambling by Scientific American
NIH on the Inside: Gambling Addiction by National Institutes of Health