Often implemented in the context of coastal resilience and in response to sea-level rise, urban shorelines are being armored at ever-increasing rates on coastlines worldwide. Engineered structures (that is, seawalls, bulkheads and revetments) are designed to mitigate risks from flooding and storm surge. While shoreline armoring can serve as an effective means of protecting people, property and infrastructure from damage, engineered ‘gray’ solutions often have unintended and cascading negative consequences to coupled human–natural ecosystems, including the coastal communities they are designed to benefit. For instance, gray infrastructure can actively degrade the marine environment by reducing habitat heterogeneity and biodiversity, which significantly dampens the plethora of ecosystem services humans receive from healthy coastal habitats. In some cases, the unintended negative consequences of shoreline armoring can be more severe in magnitude than the problems they are designed to solve.