Diffusion of innovation
Everett Rogers' theory of how new products and ideas spread through a population over time, from innovators (2.5%) and early adopters (13.5%) to the early and late majority (34% each) and laggards (16%). Adoption speed depends on relative advantage, compatibility, simplicity, trialability and how visible the results are. It is often misused as a segmentation tool, but the groups are defined by when people adopt, not by fixed personality types.
Where it's used
Used in launch planning for new categories, technology products and behaviour-change programmes. Good for asking what slows adoption, such as the cost of trying or low visibility, rather than for picking a persona to target.
Example
Making the thermostat easy to try
Illustrative scenarioA startup launches a smart thermostat that saves energy but needs installation. Early adopters buy it online, then sales stall. Checked against Rogers' factors, it scores low on trialability and visibility: nobody sees a neighbour's thermostat. The team adds free installation through energy suppliers and a monthly savings report people can share, and the mainstream market starts to buy.