Portfolio
The fund domicile is the country where a fund is legally established; it affects the fund's taxation and regulation.
The fund domicile is the country where a fund or ETF is legally established and regulated. Most ETFs traded in Europe are domiciled in Ireland (IE) or Luxembourg (LU).
Ireland offers tax advantages: only 15% withholding tax is levied on US dividends (instead of 30%), thanks to a favourable double taxation agreement with the US. This tends to lead to better returns for ETFs with a high US component.
The fund domicile can be identified from the ISIN: IE = Ireland, LU = Luxembourg, DE = Germany.
See taxes, dividends and allocation for your whole portfolio in one place.