The increasing use of AI systems raises debates about their societal, environmental and economic impacts, such as non-transparent decision-making processes, discrimination, increasing inequalities, rising energy consumption and greenhouse gas emissions in AI model development and application. Other discussions also relate to broader consequences on labour markets, consumption patterns or the market power of large corporations. This publication presents conceptional ideas for a comprehensive sustainability assessment along the AI lifecycle. We suggest sustainability criteria with corresponding indicators to encourage a systematic assessment of AI systems and to support making their development and application more sustainable.