People often use language not only for communication but also for enacting various identities to reveal diverse background information about themselves such as their geographical origin or their gender. To this end, tribe, gender, region or a country-specific dialect, accent, sociolect, vocabulary or phrases are used to construct various identities not only in face-to-face communication but also in online communication. Thus, this study aimed to investigate the strategies used by Saudi Arabian young adults to construct their different socio-cultural identities in online communication on a social website. It also aimed to study the strategies used by Saudi Arabian young adults to be polite/impolite in their online communication. The study also examined in what sense the online identity construction and politeness strategies used by the Saudi Arabian youths were similar and, at the same time, different, inter-regionally as well as cross-culturally. To this end, 158 Saudi Arabian young adults (88 males and 70 females, aged 18‚Äö-30 years, from different regions in Saudi Arabia) were selected as participants in the study. This age group was chosen as the focus of investigation as young people are more commonly involved in online interactions and communications. They took part in the study by registering on a social networking website (www.ksayouth.net) and then posting and commenting on one another's posts online. Employing a sequential explanatory design (quantitative study followed by qualitative study), the study found that Saudi Arabian youths used linguistic strategies such as region-specific words and phrases to construct regional identity, using last name as tribe name to construct tribal identity, and using religious words and expressions to construct religious identity. They constructed gender identities through linguistic strategies such as using real names (in the case of males) and using nicknames (in the case of females) due to Saudi Arabian cultural norms. They also used nonlinguistic strategies such as posting region-specific images, images of region-specific forts/castles, and images of region-specific food dishes. The study also found that the Saudi Arabian youths mostly used positive politeness strategies, including seeking agreement, giving (or asking for) reasons and presupposing /raising /asserting common ground. Negative politeness was the second most used politeness strategy employed by the participants. The youths used some new Saudi Arabian culture specific politeness and impoliteness strategies which were not described in previous literature (Brown & Levinson, 1978, 1987; Culpeper, 1996). These new strategies of politeness included: kinship non-familiar; thanking God; invocation to God; using honorific titles; courtliness; describing the other using clever and strong animal terms; comforting someone with prayers; supplicating to God; appreciation; and swearing by God. They also used some new strategies of impoliteness such as: invoking God's curse, describing the other using derogatory animal terms; using honorific titles to insult; and using religiously and socially derogatory terms. These findings imply and reflect various nuances of Saudi Arabian youths as well as the Saudi society and culture in general and as such represent new contributions offered by this study. The study also found that Saudi Arabian youths are more polite in their face-to-face communications than they are in their online communications. It was also found that Saudi Arabian youths, both males and females, who used nicknames were impolite in their social media communications. This finding may be attributed to the participants hiding behind their keyboards and not interacting with their interlocutors face to face. This study is the first of its kind in this area, and provides practical methods to partially identify online communicators and is a sound basis from which further research can take place.