One of the most important, and most studied, aspects of human perception is the act of reading. Reading has received much attention from researchers, both from a human information processing (HIP) approach and as a common, practical act that needs to be optimized, especially in the realm of human-computer interaction (HCI). One of the text variables that has been studied for over 100 years is line length, at times referred as line width. Psychologists, typographers and others working in the field of reading and advertising have demonstrated the effects of line length on readability of text. Two of the questions addressed in past studies include, How long should a column of text be, to optimize readability of the text? and Which view is more preferred by readers--multiple narrow columns or one wide column with the same amount of information content? Research has led to recommendations that line length should not exceed about 70 characters per line. The reason behind this finding is that both very short and very long lines slow down reading by interrupting the normal pattern of eye movements and movements throughout the text. In a world of personal digital devices (PDAs), one-inch cell phone displays and of wide-screen TVs and full-wall computer displays, the question of line length has renewed timeliness. Studies reviewed here show that different aspects of reading performance such as comprehension, reading speed, method of movement (e.g., paging and scrolling) and eye movements are affected by changes in line length. In addition to that, various typographic factors such as font type and size, line and character spacing as well as different screen structures such as varying number of columns and screen sizes also affect readability. These factors have an effect on optimal line length for the text read from printed or on-screen material.