Ethan Marcotte invented responsive web design as a named discipline in May 2010 through his seminal A List Apart article "Responsive Web Design." He synthesized three existing techniques—fluid grids, flexible images, and CSS3 media queries—into a cohesive methodology that allowed websites to adapt fluidly across screen sizes rather than building separate mobile sites. Before Marcotte's work, designers typically created fixed-width desktop layouts (often 960px) and sometimes a separate m.example.com mobile version. His insight was treating layout as a continuum, not discrete device targets. The timing mattered: the iPhone launched in 2007, the iPad in April 2010, and Android was gaining traction. Marcotte gave the industry a term and framework exactly when fragmentation demanded one. The core principles remain unchanged today. Fluid grids use percentages instead of pixels so columns resize proportionally. Flexible images scale within their containers using max-width: 100%. Media queries apply different CSS rules at specific viewport breakpoints, typically starting mobile-first at 320px and scaling up through 768px (tablets), 1024px, and 1440px or wider for desktops. At Ottawa SEO, we build every site responsively from day one because Google's mobile-first indexing (rolled out 2018–2020) means the mobile version is the primary version for ranking. A non-responsive site hemorrhages traffic on mobile, which is 60–70% of sessions for most Canadian service businesses. We use breakpoints informed by analytics—not arbitrary device lists—and test on real devices in Ottawa (common Android mid-range phones, iPhones, iPads) plus Chrome DevTools. Marcotte later expanded the ideas in his 2011 book "Responsive Web Design" from A Book Apart. While frameworks like Bootstrap (2011) and Foundation (2011) popularized responsive patterns, Marcotte provided the conceptual foundation. Today responsive design is table stakes, but in 2010 it was a revelation that replaced years of m-dot site headaches.