  This work introduces capacity limits for molecular timing (MT) channels,
where information is modulated on the release timing of small information
particles, and decoded from the time of arrival at the receiver. It is shown
that the random time of arrival can be represented as an additive noise
channel, and for the diffusion-based MT (DBMT) channel, this noise is
distributed according to the L\'evy distribution. Lower and upper bounds on the
capacity of the DBMT channel are derived for the case where the delay
associated with the propagation of information particles in the channel is
finite. These bounds are also shown to be tight.
