Manual assembly workers have nowadays a much higher workload than before. Not only do they have to deal with many more product variants, but as aconsequence they also receive many more information signals that they have to act upon. This study focuses on the information assembly workers receive through visual instructions. By conducting a literature review in the domains of product development with focus on design for assembly, cognition related to informationin instructions and different instruction formats like paper, tablet, and augmented reality (AR), commonalities and differences could be identified. Assembly operations are generally divided in handling a part and joining a part, and instructions should inform the assembly worker about when what should be assembled where and how. Each of these aspects has an impact on the overall complexity of the assembly process. To realise which of these aspects is most critical for an assembly worker can be of help in creating and delivering effective, tailor made instructions. The main finding is that there is not a one size fits all solution when it comes to the effectiveness of instructions, but that the type of instructions and the way they are delivered should in the first place be adjusted to the complexity of the assembly operations and secondly - if possible - also adjusted to the experience of the worker. The outcomes mentioned in this document should help laying the foundation for rules and guidelines when it comes to manual assembly instructions and its factors to consider.