At SSOFB we're firm proponents of responsive web design.  We've been developing with these principles for a number of years, and are glad this is now considered good practice.

From Wikipedia...

Responsive web design (RWD) is a web design approach aimed at crafting sites to provide an optimal viewing experience—easy reading and navigation with a minimum of resizing, panning, and scrolling—across a wide range of devices (from mobile phones to desktop computer monitors).

Ethan Marcotte coined the term responsive web design (RWD) in a seminal May 2010 article in A List Apart and it has evolved greatly since then.  We typically use the Bootstrap Framework to develop responsive websites.

Joomla 3 is fantastic for this, as many responsive features are built in.

See also...

Further reading...