While most scholars stress that translation and interpreting essentially fulfil the same function, many-especially interpreters-consider that the two are incompatible professions. In a sense, translators deal with written language and have time to polish their work whereas interpreters deal with oral language and have no time to refine their output. Any supplementary knowledge, for example, terminological or world language, can be acquired during written translation but has to be acquired prior to interpreting. A number of experimental studies were conducted by psycholinguists such as Treisman, Oleron, Goldman-Eisler and Gerver (1976). Their primary interest was the effect on performance of variables such as source language, speed of delivery, ear-voice span, noise, pauses, false starts…etc. Later advances during the 1970’s and early 1980’s concentrated on the theoretical aspects and culminated in the so-called théorie du sens. This paper tackles competence in English-Arabic translation and interpreting while highlighting similarities and differences at the textural and performance levels. It sets out by discussing the requirements of quality, audience reception, fluency and quantitative aspects of style such as output ratio and redundancy. A focal point of interest is performance constraints in simultaneous interpretation which include, among other things, personal and logistical factors, lack of a holistic approach, time lag, SL deficiencies, lexico-grammatical asymmetry as well as cultural and rhetorical divergence (including phatic communion). The study concludes with an overview of the compensation strategies employed by interpreters such as intonational clues, queuing, segmentation, approximation, syntactic adjustment, compression and ellipsis.