HIPPOCRATES is an Innovative Medicines Initiative (IMI) funded EU Consortium established to address key unmet clinical needs in psoriatic disease. As part of the project, the HIPPOCRATES Prospective Observational Study (HPOS) is a study of patients with psoriasis which will run across Europe. The study will be led by a research team at University of Oxford and supported by a team at University College Dublin. We are aiming to identify people with psoriasis who are at risk of developing psoriatic arthritis. Up to one-third of patients with psoriasis will develop a related arthritis causing inflammation in the joints and tendons. We want to identify which patients will develop arthritis with the long-term and ambitious aim of trying to prevent the development of arthritis before it occurs. We are recruiting/approaching adults with psoriasis and asking study participants to complete questionnaires every 6 months via a dedicated study website. The questionnaires will include a 'screening questionnaire' to try to identify arthritis. If participants are identified by the 'screening questionnaire' as having possible arthritis, they will be advised to seek local medical help. We will follow up with them to see if they are diagnosed with psoriatic arthritis. Alongside the questionnaire information from participants, we will ask some participants to provide a blood fingerprick sample using an easy to use at home sampling kit. The blood sample will be posted to a central location (University College Dublin) where it will be stored and then studied in the laboratory to look for markers that may predict the onset of arthritis. As many (most) participants will not develop arthritis, we are also studying the impact of psoriasis on the participants to learn more about how psoriasis affects people's daily lives across Europe.