How do you get the footer to stay at the bottom of a Web page?

To get a sticky footer:

  1. Have a <div> with class="wrapper" for your content.

  2. Right before the closing </div> of the wrapper place the <div class="push"></div>.

  3. Right after the closing </div> of the wrapper place the <div class="footer"></div>.

* {
    margin: 0;
}
html, body {
    height: 100%;
}
.wrapper {
    min-height: 100%;
    height: auto !important;
    height: 100%;
    margin: 0 auto -142px; /* the bottom margin is the negative value of the footer's height */
}
.footer, .push {
    height: 142px; /* .push must be the same height as .footer */
}

Use CSS vh units!

Probably the most obvious and non-hacky way to go about a sticky footer would be to make use of the new css viewport units.

Take for example the following simple markup:

<header>header goes here</header>
<div class="content">This page has little content</div>
<footer>This is my footer</footer>

If the header is say 80px high and the footer is 40px high, then we can make our sticky footer with one single rule on the content div:

.content {
    min-height: calc(100vh - 120px);
    /* 80px header + 40px footer = 120px  */
}

Which means: let the height of the content div be at least 100% of the viewport height minus the combined heights of the header and footer.

That's it.

* {
    margin:0;
    padding:0;
}
header {
    background: yellow;
    height: 80px;
}
.content {
    min-height: calc(100vh - 120px);
    /* 80px header + 40px footer = 120px  */
    background: pink;
}
footer {
    height: 40px;
    background: aqua;
}
<header>header goes here</header>
<div class="content">This page has little content</div>
<footer>This is my footer</footer>

... and here's how the same code works with lots of content in the content div:

* {
    margin:0;
    padding:0;
}
header {
    background: yellow;
    height: 80px;
}
.content {
    min-height: calc(100vh - 120px);
    /* 80px header + 40px footer = 120px  */
    background: pink;
}
footer {
    height: 40px;
    background: aqua;
}
<header>header goes here</header>
<div class="content">Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat. Duis autem vel eum iriure dolor in hendrerit in vulputate velit esse molestie consequat, vel illum dolore eu feugiat nulla facilisis at vero eros et accumsan et iusto odio dignissim qui blandit praesent luptatum zzril delenit augue duis dolore te feugait nulla facilisi. Nam liber tempor cum soluta nobis eleifend option congue nihil imperdiet doming id quod mazim placerat facer possim assum. Typi non habent claritatem insitam; est usus legentis in iis qui facit eorum claritatem. Investigationes demonstraverunt lectores legere me lius quod ii legunt saepius. Claritas est etiam processus dynamicus, qui sequitur mutationem consuetudium lectorum. Mirum est notare quam littera gothica, quam nunc putamus parum claram, anteposuerit litterarum formas humanitatis per seacula quarta decima et quinta decima. Eodem modo typi, qui nunc nobis videntur parum clari, fiant sollemnes in futurum.Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat. Duis autem vel eum iriure dolor in hendrerit in vulputate velit esse molestie consequat, vel illum dolore eu feugiat nulla facilisis at vero eros et accumsan et iusto odio dignissim qui blandit praesent luptatum zzril delenit augue duis dolore te feugait nulla facilisi. Nam liber tempor cum soluta nobis eleifend option congue nihil imperdiet doming id quod mazim placerat facer possim assum. Typi non habent claritatem insitam; est usus legentis in iis qui facit eorum claritatem. Investigationes demonstraverunt lectores legere me lius quod ii legunt saepius. Claritas est etiam processus dynamicus, qui sequitur mutationem consuetudium lectorum. Mirum est notare quam littera gothica, quam nunc putamus parum claram, anteposuerit litterarum formas humanitatis per seacula quarta decima et quinta decima. Eodem modo typi, qui nunc nobis videntur parum clari, fiant sollemnes in futurum.
</div>
<footer>
    This is my footer
</footer>

NB:

1) The height of the header and footer must be known

2) Old versions of IE (IE8-) and Android (4.4-) don't support viewport units. (caniuse)

3) Once upon a time webkit had a problem with viewport units within a calc rule. This has indeed been fixed (see here) so there's no problem there. However if you're looking to avoid using calc for some reason you can get around that using negative margins and padding with box-sizing -

Like so:

* {
    margin:0;padding:0;
}
header {
    background: yellow;
    height: 80px;
    position:relative;
}
.content {
    min-height: 100vh;
    background: pink;
    margin: -80px 0 -40px;
    padding: 80px 0 40px;
    box-sizing:border-box;
}
footer {
    height: 40px;
    background: aqua;
}
<header>header goes here</header>
<div class="content">Lorem ipsum 
</div>
<footer>
    This is my footer
</footer>