This paper studies {\em why} and {\em how}
Smalltalk,
although designed as a mono-user
and mono-processor programming language,
is a very good foundation for concurrent and distributed
programming.
The two main reasons behind this likely paradox are:
the rich and reusable library of classes,
and the extreme flexibility of Smalltalk.
These two specificities complement more general
object-oriented characteristics and advantages.
As examples supporting our claim, we overview  
two different Smalltalk-based software platforms for concurrent
and distributed programming.