This open-label, randomized study will assess the efficacy and safety of obinutuzumab (RO5072759) in combination with chemotherapy compared to rituximab (MabThera/Rituxan) with chemotherapy followed by obinutuzumab or rituximab maintenance in participants with untreated advanced indolent non-Hodgkin's lymphoma. After the end of the induction period, participants achieving response (Complete response [CR] or partial response [PR]) will undergo a maintenance period continuing on the randomized antibody treatment alone every 2 months until disease progression for a total of 2 years. Anticipated time on study treatment is up to approximately 2.5 years. After maintenance or observation, participants will be followed for 5 years until progression. After progression, participants will be followed for new anti-lymphoma therapy and overall survival until the end of the study.