If you lived in California, but worked in DC temporarily during 2017 (that is, you moved there but returned to California before December 31), then you will file a Resident California return and a Non-resident DC return.
The U.S. Supreme Court ruled against double taxation in 2015, stating that two or more states are no longer permitted to tax the same earnings. So, if you live in California but work in DC and pay taxes on that income in DC, California cannot tax you on it as well. California must offer you a credit for taxes you pay to DC.
If you lived in California, worked in DC, but did not return to California until 2018, then you can file two Part-Year Resident returns: One for California, and one for DC. This means you do not get a credit from California, as you will pay taxes on you California income and your DC income separately.
If you lived in California, but worked in DC temporarily during 2017 (that is, you moved there but returned to California before December 31), then you will file a Resident California return and a Non-resident DC return.
The U.S. Supreme Court ruled against double taxation in 2015, stating that two or more states are no longer permitted to tax the same earnings. So, if you live in California but work in DC and pay taxes on that income in DC, California cannot tax you on it as well. California must offer you a credit for taxes you pay to DC.
If you lived in California, worked in DC, but did not return to California until 2018, then you can file two Part-Year Resident returns: One for California, and one for DC. This means you do not get a credit from California, as you will pay taxes on you California income and your DC income separately.