Individuals with experience of homelessness, substance use/addiction, transactional sex, and incarceration experience significant health inequities across a wide range of health conditions. This inequity includes cervical cancer with individuals in these populations less engaged with both routine human papillomavirus (HPV) vaccination and cervical cancer screening programmes, yet also at higher risk of developing cervical cancer. Opportunistic vaccination is recommended by the Joint Committee on Vaccination and Immunisation for 'other at risk/vulnerable groups' who may benefit (such as people with experience of transactional sex or incarceration) at clinical discretion. However, there is limited evidence on the feasibility, uptake, attitudes and impact of vaccination in these at-risk groups and no nationally funded programme. This mixed methods exploratory study seeks to generate evidence to inform the optimal service design. Core objectives are to: 1) assess the feasibility and acceptability of offering opportunistic HPV vaccination during standard sexual health care to women at high risk of HPV and cervical cancer; 2) identify the type-specific prevalence of HPV among recruited participants; and 3) describe participants' perceptions and experiences of accessing routine HPV vaccination and cervical screening services, and/or this opportunistic (research) service. The investigators will seek to recruit women with experience of homelessness, substance use/addiction, transactional sex, and incarceration. The study will include trans-men and non-binary people at risk of cervical cancer with the same risk experiences. Potential participants will be identified prospectively via attendance at specialist sexual health services in Scotland. Participants will be offered HPV vaccination and testing, and/or an in-depth research interview. Participation can be completed within one clinic visit. The full vaccination course is available via participation (min/max does spacing 6/12 months) and participants testing positive for high-risk type HPV can/will be followed up in full and supported in accessing treatment.