Informality encompasses the ordinary and residual spaces and activities of everyday life. The notion of a perceived disorder in diverse -and sometimes underprivileged- neighbourhoods, has attracted attention in the discipline of urban design and planning with regards to the socio-spatial circumstances and cultural specificities which accommodate new relationships between public infrastructure, transitional zones and temporary, do-it-yourself informal activities, such as sidewalk vendors (Crawford, 1999; Loukaitou-Sideris & Mukhija, 2016). In ephemeral urban activities, the political vision is hidden within contradictions and possibilities that constitute “counterpractices to officially sanctioned urbanisms” (Crawford, 1999, p. 12). As a concept, informality is referring to the informal settlements of the urban environment, as much to the cultural, economic, social and political practices contributing to its organisation. 

Nonetheless, housing is one of the most indicative domains for the examination of urban informality, considering that approximately one fourth of the global urban population lives in “precarious neighborhoods” of various forms and sociopolitical contexts (Grashoff & Yang, 2020). Land occupation and informal housing has been with us since ancient times and has developed in parallel to the institution of property rights (Dikovic, 2018). In recent eras, the phenomenon is closely linked to the rapid urbanisation in the European cities and the inability of governments to respond to the emergencies and cover the growing needs such as the provision of housing, land and infrastructure (Western Cape Government, 2003). According to the OECD (2007:389), informal settlements are defined as housing units developed illegally in terms of property and/or compliance with planning and building regulations. Hence, not being conformed to legal, building and land use standards, they lack legal title and security of tenure. Moreover, various manifestations of informal settlements often share other characteristics, such as being located on the urban periphery, being self-built using local materials and financed by family savings or lending, being incrementally developed over time and finally, lacking public services and infrastructure provided by the state (International Housing Association, no date).

Informality, whether as an outcome of a conscious political action, or a byproduct of purely survival tactics, can also be understood as a form of challenging dominant knowledge and knowledge production systems. The translation of knowledge from research to practice, is a multi-scalar and non-linear process which is particularly articulated by paradigms of informal/self-help housing, shifting the focus from the role of governments to the inhabitants themselves in urbanization processes (Cociña et al, 2019). Α plurality of voices and perspectives that such paradigms exhibit is often missing in planning strategies when common policymaking and design pathways are expert-driven. In contrast to generalizing sustainable urban development indicators and goals, a crucial challenge is interpreting the harder to quantify tacit knowledge which is informally embedded in its context and its community of practice. Arguably, within the dominant Western/European epistemology, with which Southern Europe (SE) is aligned, the scope of what is considered valid, scientific knowledge and consequently practice, is often dictated by clear-cut boundaries that are shaped by the various overlapping hegemonic systems of knowledge production (Mignolo, 2009). Furthermore, the objectivity and neutrality of science and scientific knowledge has been contested over the past years both from feminist (Haraway, 1985) and Marxist standpoints (Harvey, 1974), both of which argue that scientific knowledge is dependent on the socio-cultural, political and techno-economic settings in which it occurs.

The necessity to address various disjunctures between theory and practice, or the planned and unplanned, is fortified by events such as the European-wide housing crisis and the subsequent post-financial crisis context that emerged especially in the southern peripheral regions of Europe (Hadjimichalis, 2011). The socio-economic disparities in those areas have increased (Panori et al, 2018), and the amplified need for affordable housing in post-crisis SE cities as well as the influx of economic migrants and asylum seekers, have been handled with inadequate measures of housing by the state (Maloutas et al, 2020). 

Furthermore, since the 2008 financial crisis, capitalist-driven and uneven geographical development across European regions has been investigated by scholars as a contributor to socio-spatial injustices (Hadjimichalis, 2011). Uneven development involves the uneven spatiality of capital accumulation through different processes of urban competitiveness which have contributed to the crisis, but also the social costs and environmental impacts (e.g. of climate change) which are distributed unevenly across territories. Important in the uneven development scholarship has been the exploration of how workers themselves are involved in the uneven geographies of capitalist accumulation, either through tactics of social resistance or simply by the daily struggles of adaptation and confrontation in inequality. Consequently, new bottom-up perspectives are emerging in the fields of housing and informal institutions providing new empirical evidence that has until recently been absent in planning discourse. 

Informality as evidence can indicate deficiencies in prevailing urban development paradigms and disparities in access to public amenities. Embracing informality rather than perceiving it as a challenge, can permit a more holistic understanding of an urban reality that acknowledges diversity and contradictions. The observation of such evidence can provide a different approach to the standardised vision of urban development, often pursued by city authorities. Top-down approaches often fail to decode the complexity of the reality experienced by the people on the ground and might end up with rigid proposals, not always aligned with the local voices. Participatory and bottom-up approaches can be a way to develop more inclusive, people-centred, and culturally relevant urban environments.