Assertiveness is the quality of being self-assured and confident without being aggressive to defend a right point of view or a relevant statement. In the field of psychology and psychotherapy, it is a skill that can be learned and a mode of communication. Dorland's Medical Dictionary defines assertiveness as:

"a form of behavior characterized by a confident declaration or affirmation of a statement without need of proof; this affirms the person's rights or point of view without either aggressively threatening the rights of another (assuming a position of dominance) or submissively permitting another to ignore or deny one's rights or point of view."

Assertiveness is a communication skill that can be taught and the skills of assertive communication effectively learned.

Assertiveness is a method of critical thinking, where an individual speaks up in defense of their views or in light of erroneous information. Assertive people are able to be outspoken and analyze information and point out areas of information lacking substance, details or evidence. Assertiveness supports creative thinking and effective communication.

The level of assertiveness demonstrated in any human community is a factor of social and cultural practices at the time of inquiry. These factors can evolve with time and may vary from a community to another one. For example, nowadays, in the western world, there are global public discussions about controversial topics such as drug addiction, rape and sexual abuse of women and children, which were not openly discussed in 1940.

During the second half of the 20th century, assertiveness was increasingly singled out as a behavioral skill taught by many personal development experts, behavior therapists, and cognitive behavioral therapists. Assertiveness is often linked to self-esteem. The term and concept was popularized to the general public by books such as Your Perfect Right: A Guide to Assertive Behavior (1970) by Robert Eating