ISTQB or International Software Testing Qualification Board is a well-known software testing certification board which operates on an international level. It is founded in Edinburgh in 2002. It is a non-profit association which is registered in Belgium legally.

If you are an ISTQB certified tester you can look forward to having a great career. It is standardized qualification for the software testers and the certification is offered by ISTQB. Qualifications are based on the syllabus and the guidelines for examination and accreditation. The board has more than 500,000 certifications issued.

The board consists of 58 members worldwide representing 81 countries as of May 2017. The present ISTQB product portfolio follows a Matrix approach which is characterized by Foundation, advanced and expert and the streams that acknowledge cluster of the ISTQB certification modules like core, specialist and agile.
The ISTQB stream focuses on:

Core: These are the modules that correspond to the typical ISTQB certifications and so they cover software testing topic in a breadth-first, horizontal and broad way. They are valid for the methodology, application domain and technology. They enable a common understanding.

Agile: These modules address the entire testing practices especially for the Agile SDLC.

Specialist: These modules are new in the portfolio and address specific topics in a vertical way. They can address the specific quality characteristics like security, performance, usability etc.

There are additional rules also that are summarized here:

• Foundation core is required for any Advanced level core.
• Foundation core is the default pre-requisite for the foundation level specialist certification unless it is stated otherwise in any special module. Currently, all the foundation level specialist certification needs a foundation core which is a pre-requisite.
• Any expert or advanced level specialist that is linked to lower level specialist module shall require certification though at a lower level.
• There are expert level modules that require certification at an advanced level.
• Any advanced level specialist module that is not linked with a lower-level specialist module will require the foundation core which is pre-condition.

These all set of rules are depicted from the graphical perspective for a better understand in ISTQB portfolio map.
• Expert Level modules shall require certification at the corresponding Advanced Level;

• Any Advanced Level Specialist module which is not linked to a lower level Specialist module shall require the Foundations Core as a pre-condition;

Such rules are depicted from a graphical point of view in the ISTQB Product Portfolio map. ISTQB provides a list of referenced books from some previous syllabi online.