While constructing long and yet consistent time series or composing indicators from varying sources, several stumble blocks will have to be overcome. In the ideal case we have • Stable research designs,• Timely and properly defined data from several sources or regions,• Equal frequency of data sources,• Adequate derivation of indices and • Clarity whether outliers in seasonal adjustment are to be interpreted as turning points or not.In practice these conditions need careful consideration and will often not be met. We give an overview of methods to deal with such situations. This paper has been prepared as chapter 3 of the UN handbook on composite estimators, to appear in 2015.