Bootstrap 4 Sticky Footer Not Sticking

Update 2020 - Bootstrap 4.5+

Now that Bootstrap 4 is flexbox, it's easier to use flexbox for the sticky footer.

<div class="d-flex flex-column min-vh-100">
    <nav>
    </nav>
    <main class="flex-fill">
    </main>
    <footer>
    </footer>
</div>

Bootstrap 4.0 Sticky Footer (4.0.0)
Simple Footer at Bottom Example (4.5.0)

Note: The flex-fill utility was included in Bootstrap 4.1 at later release. So after that release the extra CSS for flex-fill won't be needed. Additionally min-vh-100 is included in newer Bootstrap 4 releases.

Also see: Bootstrap 4 - Sticky footer - Dynamic footer height

Managed to figure it out. Maybe I have a misunderstanding on what "Sticky" is or something, but the solution was to change absolute -> fixed in the css file.

e.g. from:

.footer {
  position: absolute;
  bottom: 0;
  width: 100%;
  /* Set the fixed height of the footer here */
  height: 60px;
  line-height: 60px; /* Vertically center the text there */
  background-color: #f5f5f5;
}

to:

.footer {
  position: fixed;
  bottom: 0;
  width: 100%;
  /* Set the fixed height of the footer here */
  height: 60px;
  line-height: 60px; /* Vertically center the text there */
  background-color: #f5f5f5;
}

The example in the Bootstrap 4 docs has the following CSS:

/* Sticky footer styles
-------------------------------------------------- */
html {
  position: relative;
  min-height: 100%;
}
body {
  margin-bottom: 60px; /* Margin bottom by footer height */
}
.footer {
  position: absolute;
  bottom: 0;
  width: 100%;
  height: 60px; /* Set the fixed height of the footer here */
  line-height: 60px; /* Vertically center the text there */
  background-color: #f5f5f5;
}

You've probably forgotten to set html { position: relative; min-height: 100%; } - I know I usually forget that part.