  We discuss a definition of the Maslov index for Lagrangian pairs on
$\mathbb{R}^{2n}$ based on spectral flow, and develop many of its salient
properties. We provide two applications to illustrate how our approach leads to
a straightforward analysis of the relationship between the Maslov index and the
Morse index for Sch\"odinger operators on $[0,1]$ and $\mathbb{R}$.
