See also Wikipedia:Reliable sources#Using online and self-published sources

Anyone can create a website or pay to have a book published, and then claim to be an expert in a certain field. For that reason, self-published books, personal websites, and blogs are largely not acceptable as sources.

Exceptions may be when a well-known, professional researcher or notable expert in a relevant field, or a well-known professional journalist has produced self-published material. In some cases, these may be acceptable as sources, so long as their work has been previously published by reliable third-party publications. However, exercise caution: if the information in question is really worth reporting, someone else is likely to have done so.

Material from self-published sources, and other published sources of dubious reliability, may be used as sources of information about themselves in articles about themselves, so long as:

• It is relevant to the person's or organization's notability;
• It is not contentious;
• It is not unduly self-serving;
• It does not involve claims about third parties, or about events not directly related to the subject;
• There is no reasonable doubt about who wrote it.

Self-published materials (i.e. those published by the author or the author's agents) are usually reliable sources about the ideas, opinion, theories, and philosophies of those authors. Such material may be used as sources in articles about the authors, or in articles dedicated specifically to their ideas, as long as they are used only to back up descriptions of what the authors ideas are, or to quote them. They may not be used to assert or imply that those ideas are correct or good. These may be used so long as:

• It is relevant to the person's or organization's notability;
• It is not contentious;
• It is not unduly self-serving;
• It does not involve claims about third parties, or about events not directly related to the subject;
• There is no reasonable doubt about who wrote it.