A triumph in both its theoretical contributions as well as its global application, John Garrard and Ekaterina Mikhailova's dual volumes, Twin Cities: Urban Communities, Borders and Relationships over Time and Twin Cities across Five Continents: Interactions and Tensions on Urban Borders, represent a high watermark for urban studies. This innovative pair of books solidify twin cities studies as an important subfield in the field of border studies by ‘bring[ing] together scholars from across the world, drawn from urban geography, economics, sociology, history, and politics, including many leading fixtures in the twin-city field’ (2019, p. 1).

Theoretically, both volumes, which are part of Routledge's Global Urban Studies series, test a series of five variables outlined in the 2019 volume and then applied farther afield in the 2022 volume. These characteristics include interdependence, inner tension (between individual parties to the twinned or even tri-city relationships), inequality (either in terms of relative size to each other, not to mention quality of life factors, including economic, social, educational and political aspects), on-going negotiation (implying the existence of multiple systems of administration either on the local, state or international level) and resilience (a nod to the temporal trajectory of these communities as well as the effects of their interactions). The authors of the case-studies effectively apply these characteristics and their interplay throughout the two volumes – no small feat considering the books combine the efforts of over 50 scholars – but without stifling alternative models of border-city configurations, functional hierarchies and interactions, including important contributions from other theorists, including Mari Wøien Meijer's three-tiered model of functional, cultural and administrative integration (2019, p. 52). Several categories – including geographic scope, twin-city scale (examined in a discussion of paired international border cities below), temporalities, degrees of integration and subjectivities – aid the reader in reckoning with the far-reaching contributions of these books and how they are inter-related beyond their theoretical contributions.

Geographically, the editors highlight two jurisdictional variants on the twin cities: those within the same country (internal twin cities) and those that cross international borders (external twin cities). The first volume is replete with examples of the former, often drawing on familiar examples, while the second volume dips into less-well-known tandems. For example, Minneapolis–St Paul (United States), Manchester and Salford (United Kingdom), Buda and Pest (Hungary), Lagos and Ikeja (Nigeria) and Hong Kong and Shenzhen (SAR and China, respectively) constitute conspicuous pairings in the earlier volume, while Corbusier's Chandigarh (which then sprouted three urban heads), the cross-straits Italian pair of Reggio Calabria and Messina and Thunder Bay (Fort William and Port Arthur, Ontario, Canada) headline the second volume's iterations of intranational twin cities. Fascinating here are the ways in which twinning further galvanized individual civic identity, drove them further apart or served to the detriment of both individual cities where competition rendered moot most efforts at rival domination. Minneapolis and St Paul, for example, remained aloof given class considerations between the two cities – the former a city of corporate investment, banks and suits; the latter a working-class enclave united by union membership, craft production and working-class identity against elites across the river. In contrast, Chinese Communist party cadres explicitly touted Hong Kong as a catalyst for highly scaled manufacturing and investment in emerging Shenzhen, the future of the cities, not to mention that of other Pearl Delta cities yet to be determined. Finally, in Thunder Bay, Ontario, constituent opponents proceeded with head-down competition to such a degree that duplication of urban centres negated functional efficiencies that might have enhanced its regional importance.

The geographic equipoise of the two volumes is dedicated to paired cities across six (rather than five) continents, as well as the mental constructs of paired cities in China Mielville's ‘weird fiction’. These continental forays might also be classified by their economic and demographic scale. In its coverage of North America, for example, John C. Kilburn and Sara A. Buentello (2019) chronicle the breathtaking scale of Laredo, Texas, and Nuevo Laredo, Leon, where trade approximating 2 per cent of the United States’ GDP passes through the pair each year in millions of tractor-trailer loads. On the opposite scale, Clemence Leobal examines the comings and goings of a single family between Albina, Suriname and Saint-Laurent, French Guiana, in a satisfyingly intensive anthropological study of life on South American margins in the second volume. Other South American pairs of note include Omri Elmaleh's (2022) analysis of Ciudad del Este, Paraguay and Foz de Iguazu, Brazil, one of the most important, though underappreciated, trade entrepots in South America.

European city-pairs are probably the most extensively represented. Some of these include temporally distant pairs, one of medieval British towns and another a sweeping tableau of shifting borders on the Prussian frontier over time. The European Union emerges as one of the main proponents of twin cities, what with its noble objective of preventing further wars. Such studies highlight ‘Eurocities’ on the Galician (Spain)–Portuguese frontier; the Finnish–Russian paired cities of Imatra and Svetogorsk; and Haparanda, Finland, with Tornio, Sweden, perhaps the most deeply interdependent urban neighbours investigated in either book (2019). Ultimately, a significant number of studies on European cities highlight cities bordering authoritarian states –namely in Russia, as well as limited interactions between Russia and China, including at Khorgos (in both China and Kazakhstan) and the better known Blagoveshchensk, Russia, and Heihe, China. All told, these examples provide deep insight into the impact of authoritarian nation-state policies on domestic centre–periphery relations, not to mention less flexible trans-border relations.

While twin cities studied in Africa, Asia and Australia are less numerous, their contributions to understanding interdependent communities are no less significant. Anthony Asiwaju's ‘Ketu and Imejo: Yoruba twin cities astride the Benin–Nigeria border in West Africa’ (2022), for example, is a cultural and theoretical tour de force. He demonstrates with unparalleled clarity the way in which Yoruba royal enclaves provided an urban paradigm for successive cities; the eleventh-century Ketu, for example, providing a model for Imejo some three hundred years later. Asiwaju's satisfying discussion of how unique historical trajectories in the French (Benin's Ketu) and British empires (Nigeria's Imejo) during the colonial period could yield two cities identical in form but differing in economic and social differences validates the theoretical contentions of Mokhailova and Garrard's frameworks for the two books on a number of levels. The lone example for Australia, examining the Gold Coast–Tweed Heads metropolitan area, demonstrates the unique possibility of rebordering inherent in the island-continent's federalism when warranted on the regional level. The one entry for the Middle East, looking at co-operation in tourist communities on the Jordanian Israeli border, illustrates the strategic use of subtlety in carrying out mutually desirable objectives, including monitoring nautical conditions as well as provisioning employment across the border, in an ostensibly tense geo-political point of contact.

The varied temporal frameworks included in the two books raise questions about the role of history in the paired-city phenomenon. While the historical focus of several chapters highlights the impact of sweeping change on cities in Germany, the Soviet Union, the Baltic States or the former European empires, history conversely plays a subordinate role to understanding the unique trajectories of the cities as they exist today. This ‘sensitive dependence to initial conditions’ accounts in many instances for the nature of tensions between cities, the ways in which they differ from each other and their relative openness or closure to the ‘other’. This secondary role of history as a variable which helps us understand the relative position of twin cities suggests also that future steps for twin-city scholars include application of the various disciplines to improving these communities in the present.

The degrees of integration between twin cities reflects as much on the documentary and bureaucratic arc of available evidence as it does on authentic economic, social and political interdependencies. Most of the studies rely on qualitative data, heavily skewed towards planning materials, or politically optimistic interviews with city, regional or national officials. These sources tend to highlight future plans over the more subtle real-time connections that are harder to measure. India comes to mind as a place where planning (given the state's historic reliance of Soviet-style plans) has far outpaced implementation. In Garrard and Mikhailova's ‘Indian twin cities’ (2022) and Ganeskwari Singh, Simrit Kahlon and Mikhailova's ‘Chandigarh Tri-City: between conflict and co-operation’ (2022), future plans play an outsize role in potential outcomes. This is not a critique of the studies, but a reflection of what types of data are available from readily available government sources.

One related critique of the collected essays is the limited scope of subjectivities presented. As mentioned, the variety of voices largely centres on politicians and bureaucrats. The handful of studies that primarily sound out citizens rather than officials provide novel insights as to the depth of integration. Outstanding examples include Gianlluca Simi's ‘The everyday of the twin cities of Chui (Brazil) and Chuy (Uruguay): a semiotic analysis’ (2022), which employs a discursive assessment of largely cross-border economic interactions. In using a discursive critique, Simi identifies largely positive connotations in the responses of local citizens to the impact of the border. Waheed Ahmed, Muhammad Imran and Regina Scheyvens’ ‘Women's everyday travel experiences in the twin cities of Islamabad and Rawalpindi, Pakistan’ (2019) also delves into the experiences of subalterns in assessing gendered experiences of transiting between an administrative centre and the vibrant din of its commercial neighbour, Rawalpindi.

In terms of degrees of integration, results from the two volumes centre chiefly on commercial interactions, with residents on both sides of paired cities sniffing out mutually beneficial opportunities to maximize resources by selective purchasing on either side of a boundary, most notably in the market-centred interactions of Haitians and Dominicans, whose nations are notoriously antagonistic, in Lena Poschet El Moudden's ‘Ouanianinthe and Dajabon: two unequal cities on the Haitian–Dominican border’ (2022). Ethnic ties play a close second, as evidenced in Thomas Lunden's research on Latvian/Russian twins in his essay ‘Border twin cities in the Baltic area: anomalies or nexuses of mutual benefit’ (2019). Future studies might examine more deeply higher level types of integration, including shared educational resources, cross-border transfer of intellectual properties and public health services (including pest abatement and medical services). Most impressive, for example, are the ways in which EU intervention, as well as general goodwill between residents of Haparanda, Finland, with Tornio, Sweden, maximizes available resources for citizens on both sides of a border. Conversely, some essays, including Pertti Joenniemi's ‘City-twinning as local foreign policy: the case of Kirkenes–Nikel’ (2019), demonstrate the lack of integration on the Norwegian–Russian border.

Areas for future investigation are numerous. One theoretical consideration includes the question of political and economic openness as predictors of the depth of integration between cities. Open and closed pairs as defined in the current studies refer to the geographic, administrative and economic tendencies between peripheries and national centres. In contrast, politically ‘open’ or ‘closed’ systems as reflections of ideology receive little explicit attention in either of these volumes, notwithstanding the exceptional focus on administrative friction and accommodation. Having recently read the Norwegian travel writer, Erika Fatland's two books on border regions in the former Soviet orbit, Sovietistan: Travels in Turkmenistan, Kazakhstan, Tajikistan, Kyrgyzstan, and Uzbekistan (New York, 2020) and The Border: A Journey around Russia through North Korea, China, Mongolia, Kazakhstan, Azerbaijan, George, Ukraine, Belarus, Lithuania, Poland, Latvia, Estonia, Finland, Norway, and the Northeast Passage (New York, 2022), both of which examine the influence of the former Cold War combatant on contemporary society in Central Asia and Europe, there is striking resonance between the lack of functional interaction and integration between Russian or formerly Soviet border towns, especially with their more open European Union counterparts. Of course, the brilliance of the pair of books under review here is that they implicitly support the idea that authoritarian nations often have less flexible interactions with cities in open political systems; such a statement is not axiomatic. As Michel S. Beaulieu and Jenna L. Kirker remind us, Fort William and Port Arthur, Ontario, achieved nothing close to an efficient distribution of urban functions when coming together as Thunder Bay. What's more, Dandong, China and North Korea's Sinuiju historically shared educational as well as economic objectives, as illustrated in Tony Michell's excellent study (2022, pp. 173–84).

John Garrard's helpful and provocative valedictory essay to the more recent volume, ‘The twins that got away’ teases out paired communities not covered in these studies (ranging into the hundreds according to the register of the editors), as well as types of paired cities, including cities encircled by others (citing Taipei and New Taipei as an Asian example and the City of London and Westchester amidst the metropolitan mayhem of modern London as a more historical pair). A further consideration beyond the further cataloguing of case-studies would be a synthetic narrative of twin cities in historical context, taking measure of aggregated economic heft (legal and illicit), not to mention the application of these exceptional studies to the planning and improvement of urban pairs in practice. Nonetheless, this pair of books is essential for practitioners of urban planning as well as scholars in the field. If the second volume is made available in a soft cover edition they are highly recommended for classroom use at the upper end of undergraduate courses and graduate studies alike.