They operate from the 25 kV 50 Hz overhead line electrification system in both the Czech Republic and Slovakia.

Their design can be traced back to the S699.0 locomotives produced by Škoda in 1962.

ČD's cargo division (ČDC) operate the locomotives in the Czech Republic.

In Slovakia the fleet is shared almost equally between ZSSK's passenger division and ZSCS, their cargo operations.

240 121-4 to 240 145-3 were converted from S 499.1 by CSD at ŽOS Vrútky, who down-graded the maximum speed to 120 km/h (75 mph).