This paper has examined the evolution of national digital identity systems through the lens of digital sovereignty, highlighting a fundamental tension between the urgency to "solve digital identity" (Stokkink & Pouwelse, 2018) and the complex sociotechnical trade-offs that shape its implementation. At this crossroads, states are negotiating between architectures of control — which risk entrenching surveillance and data extraction — and models that centre individual agency, privacy, and autonomy. In doing so, digital identity becomes a critical site through which sovereignty is both asserted and reconfigured.

Three interrelated themes emerge from this review. First, infrastructure and technology choices — from centralised, federated, to self-sovereign identity (SSI) models — reveal deep contestations over who holds power in identity systems. States seek to reduce dependence on foreign providers and strengthen national control, yet often hybridise models to balance interoperability with autonomy. These design decisions have profound implications not only for system resilience and efficiency, but for the extent to which individuals can meaningfully exercise agency over their digital selves.

Second, governance frameworks — including legal instruments, regulatory standards, and collaborative institutions — function as mediators of digital sovereignty. While state-led initiatives often invoke transparency and accountability, this review finds that mechanisms for meaningful public participation remain weakly theorised and inconsistently applied. The Responsible Innovation framework (Anand & Brass, 2021) offers one pathway for assessing whether governance structures align with democratic values, but further empirical work is needed to evaluate its implementation across contexts.

Third, implementation and adoption practices illuminate how sovereignty is operationalised at the level of everyday interaction. Digital wallets, authentication protocols, and user interfaces are not neutral technical artefacts; they are socio-political tools that shape trust, inclusion, and access. Adoption is uneven, influenced by institutional trust, digital literacy, and the cultural legitimacy of identity regimes. Critically, this review identifies a lack of robust evidence on whether contemporary identity systems fulfil their stated objectives of enhancing inclusion and control, particularly for marginalised groups.

Taken together, these findings point to a central conclusion: digital identity systems remain “unsolved” (Naghmouchi et al., 2023). Despite substantial experimentation, no model has fully resolved the underlying “digital identity schizophrenia” (Cheesman & Slavin, 2021) — the persistent contradiction between individual control and institutional verification. Rather than offering a singular solution, this REA maps a contested and evolving landscape in which sovereignty is not a fixed attribute of the state, but a dynamic and negotiated process embedded in infrastructure, governance, and everyday use.

By synthesising a diverse and fragmented evidence base, this review contributes a structured analytical lens to understand how digital sovereignty is being enacted through identity systems. It advances scholarship on digital identity by foregrounding power, trade-offs, and political agency, and offers a foundation for more accountable and inclusive design. In doing so, it provides policymakers, technologists, and researchers with critical insights to navigate the normative choices at stake in building sovereign digital futures.