Existentialism and phenomenology are closely linked philosophies. Existentialism preceded phenomenology and is not considered a single philosophy but several schools of thought, both theist and atheist in thinking, which grew out of a reaction to traditional philosophy. The development of phenomenology is divided into three separate phases ultimately merging with existentialism. Following Second World War, the phenomenological movement gained momentum in France and encompassed many of the ideas of Edmund Husserl and Martin Heidegger. Gabriel Marcel, Maurice Merlieu-Ponty and, notably, Jean-Paul Sartre established a 'third phase' of phenomenology. This paper explores some of Sartre's ideas related to being and later applications through Medard Boss and R.D. Laing, and offers a short illustrative case vignette that shows the concepts as they might apply to nursing practice. Consideration is finally given to existential psychoanalysis as an applied research methodology