Infill development is building new housing or other development on vacant or underutilized land within existing built-up areas, rather than expanding outward into undeveloped greenfield land. Infill can include constructing on empty lots, replacing older low-density buildings with higher-density development, or converting non-residential buildings to residential use. Benefits include: efficient use of existing infrastructure (roads, water, sewer), reduced sprawl and preservation of farmland and natural areas, support for transit viability through increased density, and walkable neighbourhoods. Challenges include: higher land costs, potential conflict with existing neighbourhood character, complex approval processes, and sometimes contamination requiring remediation. Municipal planning policies increasingly encourage infill to accommodate growth sustainably. Infill debates often centre on appropriate density and design—how to add housing while respecting existing communities. Successful infill requires good design, community engagement, and infrastructure capacity to handle increased density.