Auckland Council's talking up its investments in half-year results to December.

The books show three-quarters-of-a-billion dollars were invested in key assets over the six months.

Included in that is more than $100 million on the new, Spanish-built electric trains, and $22 million on libraries.

The Council says the value of its assets has increased by $1.2 billion over the period, to $41.2 billion.

Auckland Council has maintained strong financial ratings too, including a Standard & Poor's AA.