The goal of this paper is to review the available process analytical technology tools for monitoring the batch freeze-drying process for pharmaceuticals. These systems aim evaluating in-line product temperature, sublimation flow rate, and values of some model parameters in such a way that it can be used for in-line or off-line process optimization. A detailed survey of the systems proposed in the literature is presented, grouping them on the basis of monitored variable, namely, product temperature, heat flux to the product, sublimation flux, and, finally, other variables. The advantages and drawbacks of the techniques are critically assessed, taking into account the possibility of using them not only at lab-scale but also at production scale, beside, obviously, the possibility of getting reliable measurements of the desired variables.