Machine Learning is a sub-field of the computer science and the Artificial Intelligence (AI) that provides systems with the ability to act and learn without being explicitly programmed. One of the fields where machine learning techniques have been applied with great results is the Natural Language Processing (NLP). Namely, conversational AI is a branch of NLP focused on giving computers the ability to understand and interact with text and spoken words in much the same way human beings can. ESA Virtual Assistant (EVA) is a WEB platform capable of defining, building, training and deploying customized virtual assistants to power ESA services with conversational AI skills. These virtual assistants can be defined as software agents that converse through a chat interface, so they are able to have a real conversation with the user in order to provide him/her with some kind of valuable action.