Anxiety is a common mental health problem for Canadian adolescents. Anxiety that is diagnosed as a disorder and serious enough to require treatment affects up to 10% of all adolescents by the age of 16. The median age of onset is 11 years, making these disorders some of the earliest to develop. Anxiety disorders can have serious negative effects on a young person's personal relationships, school performance, and family life. These disorders may not be discovered by adolescents, parents and health care providers. Even if anxiety disorders are discovered, adolescents may not get the right therapy. Anxious adolescents can become sick if their anxiety is not treated properly. The investigators will carry out research to test Breathe, an Internet-based treatment for adolescents with anxiety problems. Adolescents can use this treatment from home via the computer. Breathe will include information materials and personalized homework assignments to help anxious adolescents learn ways to manage anxiety. More information can be found and www.TheBreatheStudy.com

This study is a randomized controlled trial (RCT) with two groups, an Internet-delivered cognitive behavioural therapy (CBT) experimental group (Breathe) and a resource webpage (control group; considered treatment as usual for youth waiting for services). The investigators will evaluate several methodological processes and outcomes through the following objectives:

1. To determine the effectiveness of a self-guided Internet-based CBT program with limited telephone and email support in reducing anxiety symptoms among adolescents with mild-to-moderate anxiety as compared to a usual self-help intervention, a resource-based webpage.
2. To explore mediators and moderators of the Internet-based CBT program.
3. To determine the effectiveness of a self-guided Internet-based CBT program in improving quality of life as compared to a usual self-help intervention.
4. To determine adherence to a self-guided Internet-based CBT program.
5. To determine the cost-effectiveness of the Internet-based CBT program.

Inclusion Criteria:

• Score of ≥25 on the Screen for Child Anxiety Related Disorders (SCARED)
• Ability to read and write English
• Regular access to a telephone and a computer system with high speed Internet service
• Ability to use the computer to interact with web material

Exclusion Criteria:

• Positive screen on the Ask Suicide-Screening Questionnaire (ASQ)
• Positive screen on the Schizophrenia Test and Early Psychosis Indicator (STEPI; modified version)
• Score of ≥3 on the Alcohol Use Disorders Identification Test Consumption subscale (AUDIT-C)
• Residence outside of Canada