This paper investigates the cooperation of online and off-line handwriting word recognition systems. Our goal is to improve a mature online recognition system by, exploiting the complementary information present in the off-line representation built from online signal. After describing the online and off-line HMM based handwriting recognition systems, we propose a formal framework, which allows describing different strategies for combining the two HMM. These schemes are then evaluated on the UNIPEN database, both for isolated character and word recognition tasks.