Despite the fact that all translation necessarily involves a degree of uncertainty, translation theorists have show little interest in the phenomenon. The various types of uncertainty that may occur throughout the translation process are mapped out. Different aspects of the translation operation are examined, together with the various players involved, in particular the important role of the initiator, the more minor role of the author and the sometimes unpredictable decisions of the editor. The uncertainties that arise when interpreting the source text are investigated, as is the translator’s split vision between source and target. The role of the reader is also evoked, using the distinction between the model reader and the empirical reader. Attention is then focused on the various uncertainties that the translator must face when exploring the paraphrastic possibilities of reformulation in the target language. The translator’s certainties are also briefly examined. Two conclusions are drawn: the first concerns the need to devote more theoretical space to the question of uncertainty. The second underlines how this phenomenon – that professional translators have to deal with on a day to day basis – can be considered in a positive light, helping translators to remain alert during all the stages of their work.