This thesis introduces specifics guidelines to apply Web RequirementsEngineering to the treatment of Non-Functional Requirements. It introduces the process of Elicitation and Specification for Web Non-Functional Requirements and offers spreadsheets designed to capture and specify Non-Functional Requirements in the defined processes.While at present Requirement Engineering has numerous techniques and tools to identify, describe, validate and manage requirements, these are not frequently applied in the development of Web applications. The maturity of the Requirements Engineering process seems insufficient; this insufficiency demands new approaches or the evolution of current process to the correct treatment of Non-Functional Requirements. Non-Functional Requirements of software systems are not homogenous; there is a lack of consensus to answer the following questions: What are Non-Functional Requirements? How they are classified within the context of software development? and How the Non-Functional Requirements are classified within the development of web software application? This thesis starts with a revision of the state of art of the concept of Non-Functional Requirements in Requirements Engineering literature and establishes as conceptual foundations that Non-Functional Requirements are quality requirements and restrictions. Then, there is a comparative analysis of six different existing approaches in Web application development to study what treatment applies to Non-Functional Requirements, in which methodologies of the Web applications studied: Non-Functional Requirements are considered, but there is no consensus in their meaning. There are neither specifics techniques for elicitation of Non-Functional Requirements nor uniform guidelines for the specification and validation. There are no techniques supporting the treatment of the Non-Functional Requirements along the lifetime cycle. There is a lack of consensus to establish within which phase of development lifetime cycle Non-Functional Requirements are identified. There are Non-Functional Requirements that are not indentified during requirement capture and analysis phases.After this analysis and the give importance of the Non-Functional Requirements, a process for the elicitation and specification of the Web Non-Functional Requirements (quality and restrictions) is proposed, exposed spreadsheets are described to TESIS: Elicitación y Especificación de Requerimientos No Funcionales en Aplicaciones Web Rojo, Silvana iv support processes and finally, validations of the concepts and techniques are introduced applied to a real project.