Mobile technologies are used in increasingly diverse and challenging environments. With the predominantly visual nature of mobile devices, Situational Visual Impairments (SVIs) are a growing concern. However, fundamental knowledge is lacking about the causes of SVIs, how people deal with SVIs, and whether their solutions are effective. To address this, we ﬁrst conducted a convenience-sampled online questionnaire with 174 participants, and identiﬁed many causes and (ineffective) solutions. To ﬁrmly ground our initial results, we then conducted a two-week ecological momentary assessment with 24 participants, balanced by age and gender across Australia and Scotland. We conﬁrmed that SVIs are experienced often and during typical mobile tasks, and can be very frustrating. We identify a range of factors causing SVIs, discuss mobile design implications, and introduce an SVI Context Model rooted in empirical evidence. The contributions in this paper will support the development of new effective SVI solutions.