I have 2 pandas Dataframes as follows.

DF1:

Security     ISIN
ABC           I1 
DEF           I2
JHK           I3
LMN           I4
OPQ           I5

and DF2:

ISIN      ValueI2        100I3        200I5        300

I would like to end up with a third dataframe looking like this:

DF3:

Security   ValueDEF       100JHK       200OPQ       300

You can use merge, by default is inner join, so how=inner is omit and if there is only one common column in both Dataframes, you can also omit parameter on='ISIN':

df3 = pd.merge(df1, df2)
#remove column ISIN
df3.drop('ISIN', axis=1, inplace=True)
print (df3)Security  Value
0      DEF    100
1      JHK    200
2      OPQ    300

Or map column ISIN by Series from df1:

print (df1.set_index('ISIN')['Security'])
ISIN
I1    ABC
I2    DEF
I3    JHK
I4    LMN
I5    OPQ
Name: Security, dtype: object#create new df by copy of df2
df3 = df2.copy()
df3['Security'] = df3.ISIN.map(df1.set_index('ISIN')['Security'])
#remove column ISIN
df3.drop('ISIN', axis=1, inplace=True)
#change order of columns
df3 = df3[['Security','Value']]
print (df3)Security  Value
0      DEF    100
1      JHK    200
2      OPQ    300