How do I refer to the current directory in a shell script

So I have this script which calls another script in the same directory

#! /bin/sh

#Call the other script
./foo.sh 

# do something ...

For this I got ./foo.sh: No such file or directory

So I changed it to:

#! /bin/sh

#Call the other script
foo.sh 

# do something ...

But this would call the foo script which is, by default, in the PATH. This is not what I want.

So the question is, what's the syntax of doing './` in a shell script?