  This is a brief review on Brownian functionals in one dimension and their
various applications, a contribution to the special issue ``The Legacy of
Albert Einstein" of Current Science. After a brief description of Einstein's
original derivation of the diffusion equation, this article provides a
pedagogical introduction to the path integral methods leading to the derivation
of the celebrated Feynman-Kac formula. The usefulness of this technique in
calculating the statistical properties of Brownian functionals is illustrated
with several examples in physics and probability theory, with particular
emphasis on applications in computer science. The statistical properties of
"first-passage Brownian functionals" and their applications are also discussed.
