Theme Guides

Thematic investing organizes a portfolio around ideas instead of tickers. Rather than starting from “which stock should I buy”, you start from a conviction about how the world is changing, then hold the group of companies that stand to express that change. The unit of the decision is the thesis, not the individual name. If you believe AI compute demand will keep growing for years, that belief is more durable and more diversifiable than a bet on any one chipmaker, and it points naturally to a group of companies rather than a single one.

This is a different frame from the two most common ways people already invest. A broad index fund gives you the whole market and asks for no view at all. Picking a single stock takes a sharp view but concentrates the outcome on one company's specific risks. A theme sits between the two: it takes a deliberate view, an idea you can state in a sentence, but spreads it across the several companies that share the thesis, so a single earnings miss or management stumble does not sink the whole idea.

The themes collected here span the trends that are actually moving portfolios: AI infrastructure and the data center power and cooling that supports it, semiconductors, defense modernization, dividend growth for the income side of a portfolio, critical materials, robotics, nuclear and clean energy, and more. For the wider context on why investors group holdings this way, read our deeper guide on thematic investing.

Once you have picked a theme, there are two practical ways to express it, and they trade convenience against control.

• Buy a thematic ETF. One purchase gives you diversified exposure to the idea, and the fund handles the holdings and rebalancing for you. The trade-offs are cost and precision: thematic ETFs usually carry higher expense ratios than broad-market funds, their holdings can drift from the pure thesis, and a fund often launches when a theme is already popular. Each theme page lists the ETF proxies people most commonly use so you can compare them.
• Assemble the individual stocks. Holding the names yourself lets you control exactly which companies and weights you own, leave out businesses whose fit you doubt, and avoid fund fees. The cost is effort: you research each name, decide the weights, and rebalance over time. This is where a basket helps, because it turns a list of tickers into a single tracked position with target weights.

Whichever path you take, size matters more than the entry. Themes concentrate on one idea, so they tend to swing harder than the broad market. Many investors treat a theme as a satellite: a smaller, deliberate tilt sized around a diversified core of broad holdings, rather than the center of the portfolio. That way a theme can add exposure to an idea you believe in without letting a single trend drive your whole result.

In Walnut, the workflow is direct: you describe the thesis in plain language, the AI assistant proposes five or six constituents with target weights, and you fund the basket through your own connected broker. You approve every order; Walnut never trades on your behalf. Walnut is informational, not an investment adviser.

Each theme page starts from a written thesis and a clear inclusion test: a company earns a place in the theme only if its business genuinely expresses the idea, not because it is merely a large, well-known name in a nearby sector. That is why the AI infrastructure theme reaches past chipmakers into the industrials that build data-center power and cooling, and why a defense theme includes the specific primes and suppliers tied to modernization budgets rather than the whole industrials sector.

The constituents in every theme start equal-weighted, meaning each company begins with the same share of the basket. This is a deliberate default. A theme is a statement about an idea, not a claim that one specific company is the best way to play it, and equal weighting keeps any single name, especially the largest and most familiar, from quietly dominating the whole position. It also makes the performance chart on each page an honest read on the idea itself rather than a proxy for one mega-cap. Equal weighting is a starting point, not a rule: inside Walnut you set your own target weights, tilting toward the names you have the most conviction in.

Every theme page also carries a hypothetical performance line versus the S&P 500, the full roster of stocks with the rationale for each inclusion, and the ETF proxies for anyone who wants the idea as a single ticker. The stock and ETF names link through to their own guides, so you can drill from a theme into any one company and see which other themes it belongs to.

It is easy to confuse a theme with a sector, but they answer different questions. A sector is an industry classification. The widely used GICS framework splits the market into eleven of them, technology, health care, financials, energy, and so on, grouping companies by the broad business they are in. Sectors describe the structure of the market.

A theme cuts across those lines. AI infrastructure, for instance, pulls semiconductors from technology, power and cooling builders from industrials, and grid names from utilities, companies scattered across three sectors that all express one thesis. A sector answers “what industry is this company in”; a theme answers “which idea does this company help me express”. The two are complementary lenses: spreading across sectors is a way to manage concentration risk, while a theme is a way to take a deliberate view. If you want to think in industry terms instead, see our guide on how to invest in sectors.