Mirror writing (MW) is a phenomenon characterized by flipping a single letter, a whole word, or a string of letters during handwriting. The flipped handwritings can be normally recognized when projecting to a mirror. MW sometimes incorporates with mirror reading (MR), and these two phenomena are usually defined as mirror error (ME) in previous studies. Non-voluntary mirror error has been observed in children as well as patients with brain damage. Although ME has been found relating to factors such as handedness, gene, intelligence, and script system, brain mechanisms of these phenomena is still unclear and many questions are not answered: e.g., why ME occurred when children are in early stages of learning to write, and then disappeared with learning progress? If ME-associated gene leads to the failure of left-lateralization for language and thus the occurrence of ME, what’s the advantage and disadvantage of the gene type? Is there some special cognitive ability for MW children? What is the relationship between handedness, left-lateralization and language system? This paper systematically reviewed theories on MW or MR, including motor hypothesis, visual-spatial hypothesis, visual word-form hypothesis and leftward eye movement hypothesis. The existing findings in relationships between ME and factors such as handedness, intelligence, and gene were summarized, and the potential neural mechanisms underlying the generation and development of ME were also discussed. Investigations on this phenomenon will benefit our further understanding on mental processing for script-reading and writing, the acquisition of writing skill, and the principle of the object recognition system.