This longitudinal study explored the long-term effects of television viewing on the development of children's reading competencies. Among 2 cohorts of German children (N[subscript 1] = 165, N[subscript 2] = 167), measures of television viewing were collected over 4 years, and tests of reading speed and reading comprehension were administered annually. As a main result, TV genre (educational vs. entertainment programs) produced different effects. Whereas educational program viewing was positively correlated with reading achievement, relations between entertainment program viewing and reading performance were generally negative. Children who were classified as heavy viewers (average viewing time per day = 117 min) showed lower progress in reading over time as compared to medium and light viewers (average viewing times per day 69 and 35 min, respectively). Partial support was found only for 1 of the 3 tested causal mechanisms, namely television-induced reduction in leisure-time book reading.